Patrick Moore`s Practical Astronomy Series

Patrick Moore`s Practical Astronomy Series
Patrick Moore’s Practical Astronomy Series
Other Titles in this Series
Telescopes and Techniques (2nd Edn.)
Chris Kitchin
The Art and Science of CCD Astronomy
David Ratledge (Ed.)
The Observer’s Year
Patrick Moore
Seeing Stars
Chris Kitchin and Robert W. Forrest
Photo-guide to the Constellations
Chris Kitchin
The Sun in Eclipse
Michael Maunder and Patrick Moore
Software and Data for Practical Astronomers
David Ratledge
Amateur Telescope Making
Stephen F. Tonkin (Ed.)
Observing Meteors, Comets, Supernovae and
other Transient Phenomena
Neil Bone
Astronomical Equipment for Amateurs
Martin Mobberley
Transit: When Planets Cross the Sun
Michael Maunder and Patrick Moore
Practical Astrophotography
Jeffrey R. Charles
Observing the Moon
Peter T. Wlasuk
Deep-Sky Observing
Steven R. Coe
AstroFAQs
Stephen F. Tonkin
The Deep-Sky Observer’s Year
Grant Privett and Paul Parsons
Field Guide to the Deep Sky Objects
Mike Inglis
Choosing and Using a Schmidt-Cassegrain
Telescope
Rod Mollise
Astronomy with Small Telescopes
Stephen F. Tonkin (Ed.)
Solar Observing Techniques
Chris Kitchin
How to Photograph the Moon and Planets with
Your Digital Camera
Tony Buick
Pattern Asterisms: A New Way to Chart the Stars
John Chiravalle
Observing the Planets
Peter T. Wlasuk
Light Pollution
Bob Mizon
Using the Meade ETX
Mike Weasner
Practical Amateur Spectroscopy
Stephen F. Tonkin (Ed.)
More Small Astronomical Observatories
Patrick Moore (Ed.)
Observer’s Guide to Stellar Evolution
Mike Inglis
How to Observe the Sun Safely
Lee Macdonald
The Practical Astronomer’s Deep-Sky
Companion
Jess K. Gilmour
Observing Comets
Nick James and Gerald North
Observing Variable Stars
Gerry A. Good
Visual Astronomy in the Suburbs
Antony Cooke
Astronomy of the Milky Way: The Observer’s
Guide to the Northern and Southern Milky Way
(2 volumes)
Mike Inglis
The NexStar User Guide
Michael W. Swanson
Observing Binary and Double Stars
Bob Argyle (Ed.)
Navigating the Night Sky
Guilherme de Almeida
The New Amateur Astronomer
Martin Mobberley
Care of Astronomical Telescopes and
Accessories
M. Barlow Pepin
Astronomy with a Home Computer
Neale Monks
Visual Astronomy Under Dark Skies
Antony Cooke
Lunar and Planetary Webcam User’s Guide
Martin Mobberley
The Urban Astronomer’s Guide
Rod Mollise
Digital Astrophotography
David Ratledge
CCD
Astrophotography:
High Quality
Imaging from the
Suburbs
Adam M. Stuart, M.D.
With 201 figures, 142 in full color.
Adam M. Stuart, M.D.
Physician Offices of Florida City
Florida City, Florida
[email protected]
Cover photographs provided by Adam M. Stuart.
Patrick Moore’s Practical Astronomy Series ISSN 1617-7185
Library of Congress Control Number: 2005931126
ISBN-10: 0-387-26241-5
ISBN-13: 978-0387-26241-3
e-ISBN 0-387-33138-7
Printed on acid-free paper.
© 2006 Springer Science+Business Media, Inc.
All rights reserved. This work may not be translated or copied in whole or in part without the written
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to proprietary rights.
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My intellectual past was shaped by two visionary and brilliant giants of the
twentieth century, the late Dr. Carl Sagan and Sir Arthur C. Clarke, who were
instrumental in kindling a life-long interest in science and cultivating an appreciation for the greatest science fiction writing of all time. My greatest love, my children Lauren and Rachel, are my ambassadors to the future and are destined to be
stellar in whatever they do.
Technical Innovations 6-ft (1.8-m) Home-Dome. Looking southwest in author’s backyard.
Royal Palm trees further west impede the view for the first 35° in altitude.
Preface
When I was a little boy I wanted to be an astronaut or a dinosaur hunter. I was
5 or 6 years old when I received my first telescope in the late 1960s, a 60-mm
(2.4-in.) Tasco refractor. This white-and-black metal tube put me on a course to
develop a life-long interest in astronomy, and science in general. I never became
an astronaut (or a dinosaur hunter for that matter!), but I promised myself many
years ago that when I got older and could afford some decent equipment, I would
buy a telescope to rival that first 60-mm (2.4-in.) refractor.
Three short years ago I purchased a Meade 10-in. (25-cm) LX200 SchmidtCassegrain telescope. The Meade Telescope catalog had gorgeous images
obtained with this telescope and a special camera: I had never heard of a CCD
imager (charged-coupled device), but I knew I had to have one. A computerized
GO TO telescope is not necessarily the suggested first “real” telescope to own, but
I had my sights set on imaging and enough people in this wonderful hobby
confided that Meade’s was an adequate platform from which to image.
Did I mention that I live in Miami, Florida? Over the last 2 years, trading
stories on the Internet, seeking advice and answers to my never-ending questions, I have learned that there is special recognition for those who image under
the light-polluted skies of the world. Miami, like London, is right up there with
some of the toughest skies under which to image. On the Bortle Scale, my imaging
site rates an 8–9 on most nights (limiting magnitude 3 or 4: “most people don’t
look up”). Skyglow makes it difficult to collect data that are mired in the muck:
Expose for too long and many astronomical targets of interest are barely discernible above the background “noise”; expose for too short an integration and
the target of interest cannot register enough photons to adequately produce an
image. My typical sky glows a hazy orange, extending a full 60º or more in some
directions above my local horizon.
After a few weeks, the weight of my telescope and set up/break down time
became a burden: I was at risk for joining the club of newcomers to this hobby who
use their big, expensive telescopes as a living room ornament or as a hat rack after
being in the field a few times with their equipment. A permanent set up in a fiberglass dome would be perfect! I dug a hole to China, bolted a steel pier to an isolated
concrete pad, and assembled a fiberglass observatory on a concrete foundation to
enclose everything. The purchase of my first CCD camera was my final ticket to
entering the world of CCD astrophotography. Wiring the dome, a computer and
the telescope for control from my house was a dream realized for a man whose first
gaze upon our wonderful universe was through 60-mm (2.4-in.) of aperture, many
moons ago. OakRidge Observatory saw first light September 1, 2002.
This book is a synopsis of my experiences, from the planning stages of building
an observatory and making a laundry list of equipment and accessories, to finally
vii
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Preface
obtaining and processing the various images contained in this book. I am
humbled when I see the outstanding images obtained by my colleagues, many
with less expensive equipment and portable set ups. Many readers of popular
magazines such as Sky & Telescope and Astronomy might be left with the impression that high-quality images require a large telescope and dark skies. Not true!
My determination in obtaining astrophotos under difficult imaging sky conditions has rewarded me with more than a degree of self-satisfaction. All those
photons, teeming across space at mind-boggling speed for unimaginable eons,
only to find my detector positioned just right to record the event. Few imagers
have not heard people comment “Why take these photos of outer space? I can go
online and find any picture I want!” This book cannot answer that question, but
for those of us who have spent countless hours “doing what we love in the dark,”
each of us has a very personal reason for taking these images.
The inclusion of a few photos in both Astronomy and Sky & Telescope in 2004,
as well as an invitation to submit two of my astrophotos to forthcoming astronomy publications, is flattering. Most recently, in September 2004 I was chosen as
a Featured Observer in the ongoing Amateur Astronomy program at the
Smithsonian National Air and Space Museum.
There are many people I need to thank. The many friendships that have been
cultivated on the various Internet groups are a big part of the enjoyment that is
derived from this hobby. The many brains that I have picked are numerous:
There are some very knowledgeable, dedicated, and talented astroimagers out
there, setting the bar higher and higher. I want to thank the publishers Harry
Blom, Christopher Coughlin, and John Watson for their insightful discussions
during manuscript preparation, as well as Lesley Poliner, Senior Production
Editor at Springer.
Finally, my warmest appreciation goes to my wife Debi and daughters Lauren
and Rachel: many, many nights have I said “I’m going into the dome,” and what I
got in return were smiles of encouragement. “Priceless.”
Adam M. Stuart, M.D.
Miami, Florida
October 2004
Table of Contents
Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
I.
The Challenge of Imaging Under a Light-Polluted Sky . . . . . . . . . . . . . . .
1
II.
Equipment Inventory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. Telescopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. 10-in. LX200 f/10 Classic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2. Stellarvue® Nighthawk with Crayford Focuser . . . . . . . . . . . . . . . .
3. Takahashi FS 60-C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Superwedge and Pier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. CCD Camera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D. Observatory and Creature Comforts . . . . . . . . . . . . . . . . . . . . . . . . . . . .
E. Computer and Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
F. Software for Observing and Telescope Control . . . . . . . . . . . . . . . . . . .
G. Software for Image Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
H. SBIG STV Camera and Autoguider . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
I. Accessories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
J. ToUcam Camcorder . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
9
12
12
13
16
17
20
24
32
34
35
36
43
51
III.
A Night of Imaging Under the Stars (and Clouds) . . . . . . . . . . . . . . . . . . . 55
IV.
Processing Astrophotos Made Simple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
V.
A Collection of Astrophotos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
A. Solar System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
B. Nebulae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Globular Star Clusters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
D. Galaxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
E. Open Star Clusters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VI.
What to Do with All Those Photos? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157
81
82
104
129
133
144
VII. An Introduction to Minor Body Astrometry . . . . . . . . . . . . . . . . . . . . . . . 161
VIII. Invaluable Contacts and Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167
ix
x
Table of Contents
Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
Formulas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 185
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
Introduction
Another CCD (charge-coupled device) imaging book? Bear with me as I explain
why I think there will be support for yet another book on this topic. I have not
seen a CCD imaging book written for beginners, by a beginner, documenting
what can be captured under challenging skies. I own many books written by
authoritative imagers, most all of which contain stunning photos taken under
near-perfect conditions. If you are a beginner like me, you might be inspired and
will strive to become better, or be intimidated and pursue another interest. I
thought it would be instructive to publish my imaging experience because most
of us with permanent imaging setups do not have the opportunity to throw our
equipment into the car in search of pristine skies.
There are so many facets to this wonderful hobby of ours. Some of us love the
beauty and mystery of the universe and do not own any astroimaging equipment.
These people are content to view the work of others. Some of us have portable set
ups; others have permanent imaging observatories. Some of us prefer to learn
and enjoy astroimaging from the comfort of our favorite armchair, by reading
books or magazines on the subject. Some of us prefer to return frequently to our
favorite online websites, many of which whose owners have beautifully documented their journey in astroimaging. There are local astronomy clubs, planetariums, star parties, observing and imaging groups, and even astronomy imaging
camps. You get the picture. Whether you are an absolute novice or a respected
master of his craft, this hobby can be approached from many different directions
if you delight in looking at images of the universe.
Be prepared to spend some money if you are interested in taking part in
gathering those photons. Entry-level setups, ranging from portable telescopes
with piggybacked 35-mm cameras, to gorgeous Ritchey-Chretien optical
systems and professional-grade CCD cameras costing as much as a small house
are available. Do your homework, take notes, and take note of your wallet
before deciding on whether you are just putting a toe in the water or jumping
in with both feet.
I was introduced to the gorgeous images of Jason Ware, Phillip Perkins, Jack
Newton, Thierry Legault, Don Parker, and Ian King in Meade Instruments’
2000–2001 General Catalog and decided to wade into the water. I have never
looked back. Our hobby is addictive and provides instant feedback as we watch
our raw images download on a computer.
Finally, I am reminded that once in a while it is worthwhile to exchange the
camera and CCD chip for an eyepiece. Time to “stop and smell the roses.” When I
am alone in my observatory and staring through an eyepiece at a distant target,
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Introduction
or staring at a recently downloaded image on my computer monitor, you do not
have to be spiritual to be moved by the grandeur of it all. The dimensions of our
canvas are beyond comprehension. Who has not thought about the meaning of it
all, beyond the pretty picture aspect?
CHAPTER ONE
The Challenge of
Imaging Under a
Light-Polluted Sky
Light pollution is the bane of amateur astronomers, whether your interest is in
observing or imaging. Regardless of the quality of your local skies at your
imaging site, the requirement to produce good charge-coupled device (CCD)
images is the same. We want to maximize signal and minimize noise. This signalto-noise ratio, known as S/N or SNR, is the holy grail of astroimagers. Signal
(both good and bad) is the light that is recorded by the CCD chip, such as from a
galaxy or globular star cluster, along with at least one type of unwanted light
(skyglow). The exact unwanted signal cannot easily be known with certainty, but
the goal is to separate out this unwanted signal.
Light pollution and other atmospheric factors contribute to the brightness of
the sky background. Skyglow, one form of light pollution, is a key determinant in
the ability to image extended, deep sky objects. The problem is that signal, both
good and bad, builds linearly. If your mount is adequate and/or your imaging
setup is equipped for guiding, extended integrations are possible. Unwanted
skyglow, however, builds in tandem with your extended integrations. Image a
galaxy for 30 s and your raw frame has both a dim galaxy image (hopefully, at
least a dim image!) and possibly an overwhelming background glow. There are
some extended objects that will be out of the reach of your CCD chip: Despite all
of your best efforts and despite optimizing your system, skyglow will dominate
your wanted signal, making your raw frames unusable. Solar system objects, such
as the moon and bright planets, are not difficult CCD targets because integration
times are short and wanted signal is easy to capture.
Sky brightness is measured in magnitudes per square arc-second. Because the
brightness difference on the magnitude scale is a factor of 2.5 between each value,
a magnitude 16 sky background requires 2.5 times longer integration time than
when imaging under a magnitude 17 sky background, all other things being
1
2
CCD Astrophotography: High Quality Imaging from the Suburbs
equal. If imaging a galaxy using 300-s integrations is achievable with your set up,
a magnitude worsening of 1 in your sky brightness background now requires
750 s to image that same galaxy. Again, as mentioned earlier, some targets might
need to be crossed off your wish list if longer integration times are prohibitive
due to mount issues or due to background skyglow overwhelming wanted signal.
Fully two-thirds of Americans and Europeans can no longer discern our own
Milky Way galaxy with the naked eye, and of the 2500 individual stars that should
be visible under pristine, dark skies, closer to 200 stars are visible under a typical
suburban sky (Sky & Telescope press release, October 11, 2002). “Take back the
night sky” is a cry heard around the world by many of us who image under lessthan-ideal, dark skies. Several states and European countries have enacted legislation to address wasteful light that ruins our night skies. The International Dark
Sky Association (IDA), a nonprofit organization, has a website tool, DarkSky, that
allows one to input their observing site coordinates (latitude and longitude, to
four decimal places) and subsequently view the zenithal naked eye limiting magnitude. The limiting magnitude is only approximate and assumes perfect conditions, but the skies above my backyard observatory have a value of 3 to 5,
depending on weather conditions and other factors. There are plenty of nights
when the sky is cloudless, the humidity low, and the skyglow is similar to when
we are near Full Moon.
All skies, even your favorite dark sky observing/imaging site, have a minimal
background glow, produced from various sources. A typical suburban sky at
night, however, is almost 5–10 times brighter at the zenith than the natural dark
Figure 1.1. Steve Albers has compiled an image of the United States that models light
pollution. The Zenithal Limiting Magnitude for areas in red are less than 4.75 and is
considered the worst on the scale. (Used with permission, Steve Albers, NOAA.)
The Challenge of Imaging Under a Light-Polluted Sky
3
sky. If you have had an opportunity to look skyward while walking down the
streets of a populated city in the United Kingdom or in America, the sky is anything but dark, and the stars are anything but obvious in all directions. Inefficient
lighting sources and particulate matter that is suspended in the air, such as smog
and dust, contribute to this skyglow (see Figs. 1.1 and 1.2). Moisture in the air
also contributes a bit. Many of us who have chosen to migrate to the suburbs, on
Figure 1.2. This map of Europe shows levels of light pollution in the atmosphere. The
orange level indicates areas where the Milky Way is invisible; red areas indicate zones
where approximately one-hundredth of stars are visible over 30° of elevation; blue borders
indicate artificial sky brightness more than 10% that of the natural brightness, which is the
definition of a “light-polluted sky.” Yellow indicates an artificial sky brightness double that of
the natural sky background. [Used with permission; Credit: P. Cinzano, F. Falchi (University of
Padova), C. D. Elvidge (NOAA National Geophysical Data Center, Boulder). Copyright Royal
Astronomical Society. Reproduced from the Monthly Notices of the RAS by permission of Blackwell
Science.]
4
CCD Astrophotography: High Quality Imaging from the Suburbs
the outskirts of populated cities, live under a night sky that is likewise anything
but dark. The orange glow that stretches from my local horizon upwards through
60+º in some directions is a combination of mall parking lights, unshielded or
poorly aligned light fixtures, inefficient lamp sources, and security lighting that is
unshielded. Mercury street lamps, outdoor sodium vapor lamps, and neon advertising signs limit the length of individual exposures that you can take. Without a
compass, I can easily discern which direction downtown Miami is, almost
25 miles (42 km) distant, because the signature glow is strongest in one direction
(see Fig. 1.3).
There are several ways to deal with artificial sky brightness. If you have a
portable set up, nothing beats driving to a darker observing and imaging site. For
those of us with permanent setups, there are several workarounds. Imaging late
in the evening or early morning, when skyglow is diminished, is an effective but
constraining solution for those of us who must work for a living. (“early to bed,
early to rise” is the unfortunate mantra of many.) Imaging in a direction less
affected by skyglow, because most skyglow is not uniform, or waiting for a target
to climb higher in the sky and out of the glow are easy to accomplish. All successful imagers will agree that waiting for a target to approach its zenith, or transit, is
the optimum time to image anyway. Select a target that you are interested in and
use a planetarium software program (such as TheSky, Software Bisque) and time-
Figure 1.3. The orange glow of downtown Miami is unmistakable, looking North from the
author’s observatory. Polaris, the North star, is just visible in the original image.
The Challenge of Imaging Under a Light-Polluted Sky
5
skip the object until you find the transit time and date that meet your needs. The
amount of atmosphere that you are imaging through is less the higher the object
is in the sky. The reality is that although some targets never set and are always
above the local horizon, they nevertheless hug the horizon, never getting above
the glow. A few targets, such as M81 and M82, are bathed in an orange glow at my
imaging location year-round. Imaging on dark (New Moon) and transparent
nights, or when humidity is less, are further ways to combat skyglow. Direct glare,
different than skyglow, can be blocked by erecting portable partitions to shield
the telescope and camera from line-of-site intrusion.
Many astroimagers employ light-pollution-rejection filters in their imaging
train. Meade, Celestron, Lumicon, and Hutech are a few of the many companies
that manufacture these special filters. These glass filters have special coatings
that reject sodium, incandescent, and mercury vapor, reflecting those wavelengths away from the CCD chip. There is no light amplification involved; the
filter transmits the desired light of the object in which you are interested.
Unfortunately, these filters do not work on all objects. Because the wavelength
of starlight from galaxies and globular star clusters is similar to the rejected and
unwanted light, imaging these targets with a light-pollution filter in the imaging
train has diminishing returns. The goal of this filter is to transmit wanted signal
Figure 1.4. Astroart 3.0 screen capture. Single 300-s integration raw frame of the Rosette
Nebula showing good nebulosity, captured with Astronomik 13-nm Ha filter. Diffraction
spikes are artificial. Note the grainy background, indicative of noise, which can be
removed with image processing. (Used with permission, MSB Software, Inc.)
6
CCD Astrophotography: High Quality Imaging from the Suburbs
and maintain proper color balance. Different manufacturers approach this issue
differently, rejecting/transmitting light at slightly different wavelengths. The
average price for a decent filter approximates the cost of a quality eyepiece. One
downside to using a light-pollution filter is the requirement for longer integrations. Some of the blocked light is the desired light from the target you are
imaging.
The luminous haze limits one’s ability to see the stars and photograph what we
see with our naked eye or through a lens. The extended deep sky objects that we
cannot see, but that our favorite planetarium software shows us are there, are even
more challenging to filter out of the mire. Light pollution adversely affects the
ability of a CCD camera to record deep sky objects, but, fortunately, a CCD camera
can integrate longer exposures to overcome light pollution to some extent.
Light pollution adds additional background signal to individual raw images,
which must be subtracted out. Longer integration times on individual exposures
(see Fig. 1.4) and taking more exposures in order to bring out the object of interest are further requirements. When you combine images, the SNR is improved
because signal increases faster than noise. Signal increases in a linear fashion with
Figure 1.5. Astroart 3.0 screen capture. The Cocoon Nebula, even with 600-s
integrations and an Ha filter, is still a dim target under my skies. The upper left panel shows
a combined (Ha) RGB composite image. Representative channels show good signal in the
Ha and barely discernible signal in the Red and Green channels. (Used with permission, MSB
Software, Inc.)
The Challenge of Imaging Under a Light-Polluted Sky
7
each additional exposure, but noise increases as the square root of the number of
images. Some imagers adjust their histograms by raising the black point high
enough to hide any gradient that is present, but at the expense of losing faint
detail in portions of the image. Light-pollution gradients should be dealt with
first, allowing you to adjust the image histogram, which leaves a more pleasing
display of the data. See Chapter IV, Processing Astrophotos Made Simple, for
additional discussion about histograms.
If light pollution is severe or the object is too faint, the CCD chip will be saturated before a meaningful signal is recorded (see Fig 1.5). Additionally, light pollution is not uniform in images obtained with red, green, and blue (RGB) filters.
If light pollution is not uniform, the resulting gradient must also be removed
postprocessing.
Another possible work-around is to use a hydrogen alpha (Ha) filter. This type
of filter is considered a narrow-bandpass filter due to selectively capturing the
656-nm Ha light that is emitted from emission nebulae. The filter allows this
bandpass through and blocks most other light, including skyglow. High signal
can be built with extended integrations. I use an Astronomik 13-nm Ha filter
(Astronomik, Inc.) with a minimum of 300-s integrations (see Fig. 1.6).
Figure 1.6. Astroart 3.0 screen capture. Emission Nebula IC1795 is shown as a raw,
unstretched 600-s integration on the left and as a 900-s integration on the right. Five
additional minutes yields less noise and more detail, as seen in the raw image. (Used with
permission, MSB Software, Inc.)
CHAPTER TWO
Equipment
Inventory
If boating on the ocean or on your local waterways is one of your hobbies, you
might have heard the analogy that a person’s boat is like a bottomless hole in the
water: There is a never-ending list of must-have items and the hobby can be
expensive. I was reminded that the universe, which is our bottomless hole, is likewise enormous and that I might need to hold my wallet tight and keep things in
perspective as I assembled a list of “must-have” items.
A huge building with the word Tasco on it used to adorn the Miami skyline
until a few years ago. Tasco has since purchased all of the major stock of
Celestron International, and Tasco has since moved from the huge South Florida
location, but whenever I drove past the building on State Route 826, I was gently
nudged that I was “supposed to” buy that telescope that I always wanted. Tasco’s
product line was appealing to me as a child, when my needs were simple: visual
observation, easy set up, an instrument with good optical quality. Celestron’s and
Meade’s product line, however, both supported a higher performance for specialized use. When Meade’s Telescope Catalog arrived in the mail in 2001, I was
amazed at the size of some of the telescopes that amateur astronomers could purchase. It is a good thing that the catalog did not have any prices in it: I wanted the
16-in. (41-cm) Polar mounted LX200 at first sight!
Like most people who come to this hobby (or who come back to this hobby, as
was my case), I thought magnification is king. The more obvious advertisements
on most toy telescope boxes are that the optics will deliver 675× magnifications!
We have all seen this type of advertisement. Most hobbyists will agree that a practical upper limit of magnification is 30–50× per inch of aperture. I quickly learned
that it is the collection of light and a telescope’s ability to resolve an image (how
much detail can be observed through a given telescope), that are paramount. The
larger the lens or mirror, the more light that can be collected, revealing brighter
9
10
CCD Astrophotography: High Quality Imaging from the Suburbs
and sharper images. I knew I wanted a telescope for astronomical purposes (as
opposed to terrestrial observing) and I knew I should purchase a telescope that I
would not quickly outgrow. I settled on the 10-in. (25-cm) LX200 f/10 classic and
was determined to be the “uncommon observer who requires a telescope of larger
than 8-in. (20-cm) aperture for any astronomical (studies)” (Meade Catalog,
2000).
What was the size of my budget? Well, I did not have a formal spending limit,
but I allowed myself a reasonable amount given the cost of the telescope and
mount. The Meade 10-in. (25-cm) LX200 Schmidt–Cassegrain telescope is advertised as one of the “largest-selling serious telescopes in the world,” with the
ability to locate more than 64,000 celestial objects at the push of a button (see
Fig. 2.1). I decided that because I was not purchasing a toy, but a real scientific
instrument, I would call Meade and a few telescope dealers/distributors that I saw
advertised in the print media. I put together my laundry list of accessories to go
along with the big-ticket purchase (the telescope) and I additionally purchased
what I could afford. Ironically, it turned out that there was no money left over for
a CCD camera!
Figure 2.1. Meade
10-in. LX200
Schmidt–Cassegrain
telescope, on a tripod.
(Used with permission,
Meade Telescope
Instruments, Inc.)
Equipment Inventory
11
My initial list of items had a staggering bottom line of several thousand dollars.
I chose the Oceanside Photo and Telescope (OPT) dealership in California (USA)
after faxing my list back and forth with a handful of dealerships in the eastern
United States. I was comfortable with the company’s promise and written policy
of standing behind my purchase, even though the main purchase, the telescope,
was really coming from the Meade factory. I also sought the personal experience
of several colleagues on the Internet. OPT exchanged several smaller accessories
without charging me a restocking fee, as well as allowed me to test-drive Meade
Instrument’s Pictor software before deciding on Software Bisque’s TheSky.
Setting up each twilight in my backyard, without knowing the luxury of a permanently housed observatory, was fun and an adventure at first, but the finicky
weather often put a damper on my observing intentions. I learned the mechanics
of the telescope and was forced to learn to navigate the sky because I did not own
a portable computer that could be linked to the telescope.
The decision to build a permanent setup was made for me: Too many promising observing nights turned into dreary, cloud-covered evenings and began to put
a dent in my enthusiasm. What used to be fun (planning the evening observing
session while at work on my computer, while no one was looking, and racing
home to set up the telescope to do a two-star alignment) was now becoming
“pointless” as clear skies gave way to clouds and rain. I searched the World Wide
Web for statistics to support my observations: The seasonal average humidity is
73% for Miami; the average number of rainy days is 130; the average annual
monthly maximum is 83°F (28°C); the annual average monthly temperature
overall is 76°F (25°C). At night, more times than not, the weather pattern brings
clouds in from the east (the Atlantic) and can easily end an imaging session in a
matter of minutes. I reasoned that if one-third of my days were going to be rained
out, and additional nights clouded out, I estimated that due to other constraints
(family and work) I might have 5–10 evenings per month of observing and
imaging. I might as well optimize my time when the seeing was good and not
spend time and energy when the seeing was lousy. If the seeing conditions deteriorated, it was a matter of a few minutes to shut down the observatory and hope
for a better night “tomorrow.”
The following pages deal with my equipment in greater detail. I do not attempt
to compete with the necessary and excellent reading material that is available in
the numerous books and Internet articles, which the reader is encouraged to
pursue. On the subject of the LX200 telescope, for example, one only needs to do
a GOOGLE search on R. A. Greiner (Doc G.), a living legend, who has greatly
facilitated the astronomy community over the years. His knowledge and expertise
on many subjects astronomical, including the LX200, are unsurpassed. The level
of detail that is available for the electronic components alone for this telescope
can fill an entire book. The focus of this book is to allow the interested reader to
learn how one amateur brought everything to fruition in order to produce
astroimages under suburban light-pollution conditions. I certainly do not bring a
sense of authority to any subject in this writing. What I can offer are insightful
tips and perhaps provide some inspiration to other amateur imagers who are just
starting out.
12
CCD Astrophotography: High Quality Imaging from the Suburbs
A. Telescopes
1. 10-in. (25-cm) LX200 f/10 Classic
The concept of “how fast” an imaging system I should get eluded me when I
placed an order for my main observing and tracking telescope. Speaking in terms
of speed sounds funny at first when discussing optical systems, but the native f/10
system is “slower” than a wider-field f/6.3 system. Given two extended targets in
the night sky, I would theoretically be able to gather an image in less time with an
f/6.3 system than with the f/10 system that I purchased. There were work-arounds
to change the f/-ratio of my system, so I figured I could barlow (magnify) my
system for enhanced planetary views, and I could add a focal reducer/field
flattener to grab wider-field views quicker. Purchasing an f/10 system would be a
good compromise to be able to do both planetary imaging and deep-space
imaging.
The 10-in. (25-cm) aperture LX200 Schmidt–Cassegrain telescope (SCT,
Classic, 3.34 ROM software) is a catadioptric (mirror–lens) design, compact in
size but with a long focal length. The worm-gear motor-drive system has enough
precision to enable long-exposure guided photography. Theoretical pointing
accuracy is 0.333 arc-seconds (1 arc-second is 1/3,600 of a degree). With the
motor engaged, the telescope tracks at a precise sidereal rate required to track the
stars across the sky. The electronics of the LX200 are integrated in the forkmount design, and “observatory-level” precision in tracking, guiding, and
slewing are claimed by Meade.
P.E.C. training (correcting periodic error due to imperfections in the right
ascension (R.A.) drive worm gear) is mandatory. This greatly enhances the
east–west drift accuracy of the LX200. Declination drift can also be corrected, but
an accurate polar alignment is an absolute must. Phillip Perkins has an excellent
tutorial on polar aligning the LX200 (see Chapter VIII). Polar alignment refers to
aligning the rotational axis of the telescope mount with the rotational axis of the
Earth by adjusting the equatorial wedge to which the telescope is mounted. We
forget that we are imaging from a rotating Earth: Long exposures will show star
trailing if the telescope’s drive did not track at sidereal rate or if the R.A. axis
were not properly aligned. On a permanent pier, doing a good polar alignment
once will retain its alignment for many months. Periodic maintenance on the
alignment can be checked with yet another routine called the Drift Method, which
is also referenced in Chapter VIII. I like Chuck Vaughn’s easy-to-understand
treatment of this topic.
Collimation is also a requirement of this telescope design. This term refers to
optically aligning the two mirrors. On a permanent pier, the alignment can hold
for many months but should be checked before critical high-resolution imaging
of the planets. Any maladjustment of the imaging train will diminish the quality
of the images.
Because the telescope is permanently mounted, each imaging session begins
easily enough with making sure that the time and date are accurately set in the
keypad, confirming that the keypad selection is set for the telescope being in
polar alignment mode, and then synchronizing on a known star that is visible.
Equipment Inventory
13
This is all that it takes for the telescope’s computer to know where I am in the
world and where every cataloged object in the computer’s memory is in relation
to my observatory site. Pretty awesome. In a later section, I discuss available software that allows integration of the telescope with a much expanded catalog of
asteroids, comets, and extended targets.
The keypad allows access to an enormous library of targets in the night sky.
Messier objects, planets, galaxies, distant nebulae, and tens of thousands of stars
are available from several popular catalogs. Enter the name, coordinate, or designation of an intended target, press a button, and the telescope slews to the object
at up to 8° per second. Depending on the quality of one’s telescope, the object, if
not centered in the field of view (FOV), is within the field each time.
The mirror–lens design is a bit problematic when focusing. The focus knob controls the position of a primary mirror as it moves along a greased baffle. Due to the
lateral movement of the mirror when focusing, an object that is initially centered
in the FOV will sometimes fly out of the field with a change in focus position,
something Meade does not advertise. Meade jumped on the bandwagon of aftermarket electric focusers and now includes both their microfocuser and mirrorlock design on their new and improved GPS LX200 units. I chose a JMI NGF-S
electric focuser (Jim’s Mobile, Inc.), which, instead of moving the primary mirror
of the telescope to achieve focus, moves the eyepiece (or camera) draw tube, which
leaves objects centered in the eyepiece or on a CCD chip despite a change in focus.
The aftermarket purchase of an electric focuser, which does not attach to the telescope’s focus knob, is an important accessory to purchase if you own an SCT telescope, whether observing or CCD astrophotography is your interest.
Another useful aftermarket design for the LX200 classic, since incorporated in
the newer GPS unit, is a mirror-lock bolt, which allows the primary mirror to be
safely “locked down” after achieving rough focus. Tweaking fine focus is achieved
by use of the JMI focuser, in my case.
Rod Mollise’s Choosing and Using a Schmidt–Cassegrain Telescope (Springer,
2002) is a must-have reference that goes into great detail about all aspects of SCT
design and use, including the LX200.
2. Stellarvue® Nighthawk with Crayford
Focuser (Formerly Known as SV 78-S
Refractor)
A piggybacked refractor telescope is a necessary purchase for several reasons
when the primary telescope is a long-focal-length LX200 (see Fig. 2.2). A refractor
can provide wide-field images while guiding through the LX200, and guiding
through the refractor is possible when imaging through the LX200. Wide-field
images reveal sweeping views and place objects in context, but there might be
little detail revealed. Some of the galaxy images in Chapter V, for example, are
interesting because of their size contrasted against the enormity of the stellar
background. In both cases, the LX200 provides a reasonable tracking mount. The
Stellarvue® line of achromats is very popular in the astronomy community.
Stellarvue® specializes in making hand-crafted refractors with excellent optical
14
CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 2.2. Piggybacked Stellarvue Nighthawk and Meade LX200. The large blue metal
dew shield on the LX200 almost extends out of the observatory. The blue attachments are
infrared detectors, part of the Dome-Works™ system. A small Meade guide scope is to the
left of the refractor. Black heating straps circle the dew shields of both telescopes and are
part of the Kendrick Dew Heater system. (Used with permission, Stellarvue® Telescopes, Meade
Instruments, Technical Innovations, and Kendrick Astro Instruments, respectively.)
Equipment Inventory
15
quality. The company has a reputation for delivering quality products and has
excellent customer service. The Stellarvue® Internet user group is one of the most
mild-mannered groups out there, with never a sour note aimed at the manufacturer or product line. I cannot think of another group or product line that is in
the same company.
The Stellarvue® Nighthawk is a pearl-white achromat that includes a 2-in.
(5-cm) JMI Crayford focuser as an upgrade (see Figs. 2.3 and 2.4). A Crayford
focuser is a type of telescope focuser in which the focus tube is moved by a roller.
It is noted for smooth, slack-free motion and for precisely adjustable friction. The
aperture is 80-mm and it has a fast f/6 design. Color correction is considered
“good.” The biggest drawback with most any achromat is the way the telescope
focuses blue light in a plane different from where red and green are brought to
focus. This leads to some “blue bloat,” which describes stars that are fat and less
than pinpoint. This phenomenon is discussed in a later section.
Figure 2.3. Stellarvue Nighthawk mounted on Losmandy dovetail plate and DR 125-mm
rings, all secured to LX200. The Starlight Xpress™ HX916 camera and Astronomik filter
drawer are seen at the lower left. (Used with permission, Stellarvue® Telescopes, Losmandy
Astronomical Products, Meade Instruments, and Astronomik, Inc., respectively.)
16
CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 2.4. The
business end of the
Meade LX200 and
Stellarvue Nighthawk
refractor. Corrector
plate glass with central
secondary mirror
housing is shown on
the LX200. The three
round screws are used
to collimate the mirrors.
The Stellarvue
Nighthawk has two
perpendicular metal
wires just inside the
dew shield lip, which
are used to create
artificial diffraction
spikes to assist in
focusing. Infrared
detectors, part of
Technical Innovations’
Dome-Trak™ system,
can be seen on each
side of the LX200. (Used
with permission, Meade
Instruments, Inc., Stellarvue
Telescopes, Inc. and
Technical Innovations, Inc.,
respectively.)
3. Takahashi FS 60-C
I had the pleasure of owning my first apochromatic telescope (albeit, sporting
only 60-mm of glass aperture) for a few months. The Takahashi refractor is a
fluorite apochromatic refractor and the Takahashi line is considered one of the
finest in the industry. I purchased the Takahashi FS 60-C intending to use it as a
wide-field imaging scope and found it almost completely free of chromatic aberrations, with little color focus shift when using my Astronomik Type II filters. I
found a slight bit of blue misfocus, which required the use of a Schuler–VIR filter,
similar to when imaging through the Stellarvue Nighthawk. The FOV is extremely
wide when used with the Starlight Xpress™ HX916 camera (a whopping 67 × 85
arc-minutes) and provides for nice framing of large nebulae regions and open
star clusters.
Equipment Inventory
17
B. Superwedge and Pier
When it comes to astrophotography, the altitude/azimuth mount becomes a
shortcoming due to field rotation. To do proper astrophotography with a forkmounted telescope, you need to tilt the forks to your latitude. The best way to do
this is with a wedge (see Fig. 2.5). When the telescope is turned on, assuming an
accurate polar alignment, objects will stay in the FOV because the mount is tracking at a sidereal rate (one Earth revolution per 24 h). By turning in R.A. (from
east to west) the telescope drive counters the turning Earth.
The Meade Superwedge is both a godsend and a curse. This very heavy apparatus [25 lbs (11 kg)] sits on top of the Astro Pier™ (see Fig. 2.6). The problem with
the Superwedge out of the box is that there is sloppiness in both the R.A. and
azimuth adjustment. The Mitty, Milburn, and a few other wedges are more precisely engineered than the Superwedge. In my opinion, this only makes a difference when adjusting the wedge. Once the wedge is permanently mounted and
precisely aligned, the Superwedge is a stable platform. The problems with the
Meade Superwedge involve making fine adjustments rather than a lack of stability. A few modifications to the Meade wedge will make it more adjustable as well.
These modifications are described in the Meade Advanced Product User Group
(MAPUG) archives (which can be found online, see Chapter VIII) in great detail.
For a permanent installation, and if you have the patience to set it up carefully,
the Meade Superwedge is fine.
Modification examples include replacing all of the bearings with special bushings and nylon washers, replacing all of the hex socket screws with T-bolts, and
replacing the azimuth threaded dog (the metal piece that locates in the slot and
Figure 2.5. Meade
10-in. LX200 f/10
Classic, mounted on
Meade Superwedge
and tripod. (Used with
permission, Meade
Instruments, Inc.)
18
CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 2.6. LX200 drive base attached to Superwedge and Astro Pier™. Take note of the
angle at which the drive base is attached to the wedge tilt-plate (26° for my latitude).
Equipment Inventory
19
pushes the wedge side to side) with a longer one with a closer fitting thread so
that it does not “twist” (a fault contributing to backlash). Any and all of these
modifications are reported to make a significant improvement in the ease and
reliability of accurately setting up. On a modified Superwedge, turning either the
altizmuth or azimuth knob results in a smooth and precise movement of the star
in an eyepiece. There is no backlash. This is how the factory version should work,
but does not. Again, however, a polar mounted telescope once adjusted needs
tweaking only rarely and the solid mount that it is makes the Superwedge a great
piece of equipment to have.
My Le Sueur Astro Pier™ (Le Sueur Manufacturing Company, Inc.) eliminates
the task of having to level the telescope and line up on North before each observing session (see Fig. 2.7). It offers excellent rigidity to virtually eliminate vibration
Figure 2.7. Schematic of Le Sueur Astro Pier, with mounting J-bolts depicted as having
been set in concrete. (Used with permission, Le Sueur Manufacturing Co., Inc.)
20
CCD Astrophotography: High Quality Imaging from the Suburbs
from accidental jarring, which makes it an excellent choice for precision guiding.
Whether you have the need for precision astrophotography or just like to sit
down for a few hours of visual observation, a permanent-mounting pier is the
perfect choice. The Aurora model Astro Pier is manufactured to accommodate
larger fork-mounted telescopes. Being of industrial quality, this pier has the
rigidity demanded by larger telescopes and those that have a high-use application. The rigidity ensures that for a given force, vibration dies out quickly. Bolt
holes in the pier’s base allow for leveling of the entire pier and mount by simply
adjusting the nuts on the mounting bolts.
The pier is isolated on a concrete pad from the observatory floor with 0.5-in.
(1.3-cm) thick felt pads on all four sides. Manufactured of steel with fully welded
seams, the Astro Pier is rugged and durable. Four coats of white Rustoleum
Industrial Enamel™ are applied, so the finish is pretty and durable for weather
resistance. The vertical tube has an outside diameter of 6-in. (15-cm) and a wall
thickness of 0.25-in. (0.6-cm). The pier base plate is 0.5-in. (1.3-cm) thick and
14-in. (36-cm) in diameter.
My finished pier is 30-in. (76-cm) tall and is mounted slightly off center, just
north of the dome’s center. The mounting plate has a bolt pattern that matches
the bottom of the Superwedge. A mounting bolt kit contains all the necessary
installation hardware, as well as a template for the installation of the pier. Le
Sueur ships the kit in advance of the pier so that the concrete footing and
J-mounting bolts can be prepared in advance, cured and ready to accept the pier.
I dug an 18-in.-wide × 36-in. deep (46-cm-wide × 91-cm-deep) hole in order to
pour the concrete footing (see Fig. 2.8).
I ordered an electrical outlet installed on the pier, as well as an accessory shelf.
I had to hand-tap the holes for the machine screws in order to mount the shelf,
but the convenience of having a shelf was worth it.
C. CCD Camera
A little history first. The CCD camera was developed at Bell Laboratories more
than 30 years ago. CCDs have the ability to record objects too faint for the eye to
see. The CCD is a silicon chip recessed behind a clear optical window. The rest of
the camera comprises electronics to record and digitize the signal, plus a cooling
system. There is no viewfinder! The Voyager spacecraft, which lifted off from
Earth 28 years ago, the current Cassini spacecraft orbiting Saturn and its moons,
and the two rovers currently on the surface of Mars—all of the stunning pictures
that have been transmitted back to Earth have been imaged with a CCD camera.
The basic design consists of an array or matrix of light-sensitive regions called
pixels (1 pixel = 1/1000-mm, or about 4 ten-thousandths of an inch). The light
from distant objects, after teeming across time and space, is recorded on the
detector as electronic signals at each pixel element site. A computer that the
camera is connected to subsequently counts the electrons and processes the data
as an image of light and dark regions.
The CCD cameras have several advantages over traditional film cameras, the
most important of which is a greater sensitivity over film emulsion. The almost
Equipment Inventory
21
18"
36"
Dig hole approximately 18" x 36" deep.
Fill hole with concrete. This will take
approximately eleven 80 lb. bags of
Quickrate. Note: The last four of
these bags will need to be mixed to
the consistency of 6* slump* concrete.
Assemble mounting bolts and waferboard templates.
Place mounting bolt
assembly into concrete
and level across the
top of the waferboard
templates. Make
certain that the bottom
waferboard template
is pressed down
firmly across the top
of the wet concrete.
*Slump is measured in the amount of fall in inches
when a slump form is removed. Originally, this
measurement was acquired by placing the mixed
concrete into a 12* deep, 1 U.S. gallon bucket.
When the container was removed, the amount
of fall, or slump was then measured.
Figure 2.8. Schematic of mounting template that supports a Le Sueur Astro Pier. (Used with
permission, Le Sueur Manufacturing Co., Inc.)
instantaneous display of one’s images on a computer screen after downloading
from the camera means that no film needs to be dropped off for processing.
A Starlight Xpress™ HX916 camera was my first CCD camera purchase (see
Fig. 2.9). When this camera was first introduced, it was advertised as the world’s
first megapixel CCD camera, with a fast USB connection. The HX916 is a highresolution monochrome camera that comes with proprietary software for image
22
CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 2.9. Starlight Xpress HX916 camera and USB control box. The USB control box is
attached with Velcro to the west fork arm of the LX200. (Used with permission, Starlight
Xpress™.)
acquisition and minimal image processing. The USB connection is approximately
three times faster than a parallel port connection, and download times for
unbinned 1×1 images are on the order of 11 s. Unbinned images are a large 1300 ×
1030 pixels, and each pixel is 6.7-µm on a side (1-µm = 1/1000-mm). The camera
is fairly light, a mere 4-in. (10-cm) long, and just over 2.3-in. (6-cm) wide. The
CCD array is a Sony ICX085AL chip that has a spectral response curve typical of
most amateur CCD chips: it peaks in the visible range (roughly 400–600-nm
wavelengths) with some sensitivity in both tails (ultraviolet in the left tail,
infrared in the right tail). Sensitivity in infrared (IR) (~700–900-nm wavelengths)
is the reason that many imagers employ an IR-blocking filter when doing
trichrome imaging with an achromatic refractor. (see Fig. 2.10).
Software driver installation for the camera is not necessarily straightforward or
user-friendly. The installation sequence is supposed to complete with minimal
user interference, but installing the software on a computer running Windows XP
home edition or on a computer running Windows Me was a several-day chore.
Soliciting opinions on the Internet, I found many people with the same installation issues. Device Manager conflicts, hex file incompatibilities, and Block I/O
issues are some of the sticking points during installation. Terry Platt from
Equipment Inventory
23
1.0
0.9
Relative Response
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
400
500
600
700
800
900
1000
Wave Length [nm]
Figure 2.10. Spectral response curve of the Sony ICX085AL chip. The profile displays the
fairly typical peak response in the visible range of 400–600-nm wavelengths. (Courtesy of
Sony Electronics, Inc.)
Starlight Xpress provided decent support in a timely fashion via email, and the
Internet user group for Starlight cameras was also a tremendous help.
The quality of the downloaded images is impressive because of good quantum
efficiency (QE), which describes a camera’s response to different wavelengths of
light. An ideal QE of 100% would mean that the conversion of photons to electrons was complete. The QE of the Sony chip in the Starlight Xpress HX916
camera peaks at 48% in the green. Depending on local imaging conditions,
matching dark frames are rarely needed, but a bias frame is recommended. Both
types of images are discussed later.
Matching a CCD camera to a telescope is important in order to optimize the
resolution that your optics can deliver. You still need to take into account your
local seeing conditions. Table 2.1 illustrates the LX200 and Stellarvue refractor in
various configurations with the CCD camera (Table 2.1). Unbinned images with
the LX200 are practical only when used with the Meade 3.3 focal reducer. When
the image scale is less than 1 arc-second/pixel, images are said to be oversampled
(i.e., the pixels are too small for the optical configuration). When the scale is too
large (say, very much larger than 4–5 arc-seconds/pixel), the image is said to be
undersampled and stars can appear square and blocky.
24
CCD Astrophotography: High Quality Imaging from the Suburbs
Table 2.1. LX200 and Stellarvue Nighthawk in Various Configurations with a CCD
Camera
Telescope
Chip Array
(pixels)
SX HX916
camera
Pixel
Size
(microns)
10″ LX200 f/10
10″ LX200 f/6.3
10″ LX200 f/3.3
80mm SV
Nighthawk
1300
1300
1300
1300
×
×
×
×
6.7
6.7
6.7
6.7
1030
1030
1030
1030
Field of
View
(arc-minutes)
9.5
15
28
49
×
×
×
×
12
19
36
62
Image Scale (arc-sec/
pixel)
Unbinned 1×1 Binned 2×2
.55
0.88
1.67
2.88
1.1
1.75
3.34
5.75
D. Observatory and Creature
Comforts
The purpose of an observatory is to protect the equipment from the elements,
provide a place of comfort for the observer, and allow efficient use of the equipment by not having to spend a lot of time setting up for a night of imaging or
observing. Amateur astronomers dream of having their own observatory, a site
with dark skies and good seeing. One out of three was in the cards for me. I spent
a lot of time designing my observatory (or as my kids called it, a la-BOR-atory,
such as they hear the cartoon character Dexter pronounce it). I did a GOOGLE
Internet search for amateur observatories and saw a multitude of design choices,
both prefabricated and do-it-yourself. Did I want a roll-off roof design? Did I
want a square building similar to a converted tool shed? Did I want a dome
shutter that opened outward, on a hinge? Nah! I wanted a white, fiberglass observatory with round walls, a dome top, and a real working electric shutter because
this design looked absolutely cool! This is the traditional observatory design that
most people envision when you mention that you have an observatory. Mt.
Palomar, on an affordable scale, in my backyard.
Technical Innovations, Inc. was founded by John and Meg Menke more than
a decade ago, a delightful husband and wife team who made the entire selection
process a breeze. I found their company advertised in the pages of Sky &
Telescope and also found their website on the Internet. Jerry Smith, who is
molded from the same character as the Menkes, has since taken the reins of the
company. The structure is a fiberglass product designed with the budget of
amateur astronomers in mind. Several diameters are available, from 6-ft
(1.8-m) to 15-ft (4.5-m), as well as the ability to customize colors, add cubbyholes built directly into the circular wall, add extensions to increase the height
of the walls, automate the dome, and so on. A very detailed At Home in a Dome
handbook (Technical Innovations, Inc., 1996) is available on the Technical
Innovations website, and I was able to read the basics of observatory design,
form, and function before placing an order. I selected the 6-ft (1.8-m) Home
Dome with one PC computer cubby. A cubby is 30-in. wide, 16-in. deep, and
40-in. high (76.2-cm wide, 40.6-cm deep, 102-cm high) and increases the dome
Equipment Inventory
25
Figure 2.11. Windlass and steel cable on rear cover of shutter (Technical Innovations,
Inc.) Weight plates on bottom of the LX200 balance the telescopes and camera. Notice the
5-lb (2.3 kg) strap weight attached to the LX200 east fork-arm, which assists in tracking
across the sky.
26
CCD Astrophotography: High Quality Imaging from the Suburbs
floor area by providing a recess in the wall. The walls of the dome are 45-in.
high (1.1-m).
An Astro Pier is installed slightly off-center in the north direction. An SCT telescope in equatorial configuration on a Meade Superwedge and I easily fit within
Figure 2.12. Plastic cover that dampens the sound of the dome rotation motors when they
are engaged. The wires are attached to copper contacts and allow the motorized shutter to
operate only when the dome has rotated to the neutral or home position. (Used with
permission, Technical Innovations, Inc.)
Equipment Inventory
27
the more than 32-ft2 (2.9-m2) of floor space. I decided to motorize the dome
shutter, which consists of three panels, two of which move up and over, automatically disengaging during opening to nest together at the rear of the dome when
opened. A 12-V DC motor controls the shutter windlass and stainless-steel cable
system (see Fig. 2.11). The shutter width is 30-in. (76-cm) and the slot opens
10-in. (25-cm) past the zenith. Dome rotation is accomplished with two 12-V DC
motor drive systems, each fitted with a plastic sound-suppression cover. The
covers were an afterthought and hide the unsightly motors, in addition to
suppressing their noise. (see Fig. 2.12). Dome-Trak™ is a proprietary system that
links the telescope and dome slot position via infrared technology. Infrared
sensors placed on the telescope tube allow the slot opening to frame the front of
the telescope aperture. The power supply is a 12-V 10-A system with a built-in
key switch and two toggle switches for dome rotation and shutter operation (see
Fig. 2.13). Dome-Dial™ is another electronic system that monitors and displays
the azimuth direction of the observatory dome (see Fig. 2.14). A sensing wheel
detects movement of the dome and reads the position relative to the starting,
or home, position. With the slot aimed North, the azimuth position is 0.
Communication between the observatory computer and telescope is accomplished via Ethernet cable from my house.
Choosing a location for the observatory on my builder’s half-acre (0.2 ha) lot
was an important first step. I live in a residential community bound by the rules
Figure 2.13. Technical Innovations power supply box, relay box, and a wall-mounted
hygrometer.
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CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 2.14. Dome-Dial display unit and relay box, mounted on observatory wall. Blackand-white security camera is also shown. (Used with permission, Technical Innovations, Inc.)
of a homeowner’s association board: I wanted the dome set back far enough from
fence lines [6-ft (1.8-m) minimum] so as not to cause any easement problems,
and I chose the planting location of all of our palm trees so as not to impact the
view to the east or north. I additionally had to apply for a building and electrical
permit. Constructing an observatory as an accessory building on a concrete pad
was an easy building permit to get.
Polaris, the North Star, is visible from my yard in a few unobstructed locations,
and the southwest corner of the yard is where everything came together for the
right reasons (see figs. 2.15 and 2.16). Unfortunately, this meant digging a 150-ft
(45-m) trench, by hand, from my home office (the control room) to the observatory for the electrical and cable! I marked the footprint of the observatory in the
grass, hand-excavated a 16-ft3 (0.5-m3) hole for the pier’s footing, and poured the
concrete for the J-bolts of my pier. The concrete footing thus directly contacts
the soil supporting the entire pad. The hole was dug 36-in. (91-cm) deep and
improved the resistance of the pier to side motion and vibration. The relative
effect of the “off-balance” equatorial mount is reduced by the mass and size of the
concrete footing [roughly 2400 pounds (1090 kg)]. Additionally, vibrations transmitted through the soil cannot move the large mass of the pier footing to any
significant degree.
Equipment Inventory
29
Figure 2.15. Technical Innovations 6-ft (1.8-m) Home-Dome, looking east in author’s
backyard. Alexander Palm fronds extending above the shutter in the photo are 20-ft (6-m)
away and impede the view for the first 20+° in altitude.
For several weeks, the odd-looking white pier stood waiting to be enclosed by a
dome, but the birds found another use for it. I laid and braced separate runs of
polyvinyl chloride (PVC) conduit for my electrical and cable from my house to
the observatory site. Cat 5e Ethernet cable would network my home office personal computer (PC) with the observatory’s PC, and I left room in the conduit for
a run of video cable. The observatory pad would be 12-in. (30.4-cm) larger on all
sides than the observatory structure in order to protect the fiberglass from lawn
mowers striking the walls. The soil under the pad was firmly compacted (handtamped) and leveled. I distributed a layer of crushed stone over the dirt to
promote better drainage and then laid a sheet of polyethylene plastic as a moisture barrier between the soil and concrete foundation. After firmly bracing wood
planking at 12-in. (30.4-cm) intervals with metal stakes, in the outline of the footprint of my observatory walls and cubbyhole, I added plenty of rebar and coordinated the delivery of a cement mixer to deliver the concrete. I had to wheelbarrow
the concrete to the observatory site because the truck would not fit through my
gate. Delivery of concrete for the intended purpose was a first for the company:
The driver got a big kick out of finishing the concrete surface for me “just right.”
I removed the wood planking forms after 12 h and beveled the edge of the concrete where it met the forms in order to promote water drainage off the pad. I
30
CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 2.16. Technical Innovations 6-ft (1.8-m) Home-Dome, looking north in author’s
backyard. Various palm trees and a distant Rainbow eucalyptus impede the view for the first
20+° in altitude.
covered the concrete with plastic sheets for a few days in order to retain moisture
and not cause rapid drying of the surface. When a concrete surface dries too
quickly, the result is excessive concrete dust.
A month later, the fiberglass observatory arrived by freight and was soundly
packed in a large wooden crate. The estimated weight of the crate was close to
700-lbs (318-kg). Shipping within the United States is via a freight carrier with
“tailgate” service. This service entails gently placing the 700-lb (318-kg) crate on
the tailgate of the truck and it is up to the owner to arrange for the crate to travel
from the tailgate to the garage floor, for example. International shipping is also
available and can be arranged by Technical Innovations, Inc. for either air or
ocean shipping. Unfortunately, additional duty and taxes must be shouldered by
international customers. I was at work when the delivery truck arrived at my
door; for $50.00 (27£) additional, I told my wife to make sure the delivery man
found a way to get the crate safely into my garage, where it sat unopened for a few
days because I did not own a crowbar!
The unassembled fiberglass observatory consists of two dome halves, a rear
cover and shutters, dome support rings, three-piece 45-in. (114-cm) high walls,
three-piece base ring, a molded full-height entrance door, and all hardware,
caulk, and a detailed instruction manual. The manual comes in a three-ring
Equipment Inventory
31
binder and is written in standard English with numerous supporting photographs
and schematics of the observatory construction.
The walls were assembled first and thankfully fit on the concrete foundation as
measured. Assembled, it looked like a hot tub from a distance. This lessened the
chance for raised eyebrows from the neighborhood patrol. The dome walls have a
reverse flange that was secured to the foundation with lag bolts and concrete
anchors. I used a 0.5-in. (1.3-cm) masonry bit and some elbow grease. I drilled
small pilot holes first to maximize the location of the hole. I also injected expanding foam under the base ring in order to better achieve a watertight seal with the
observatory walls and foundation. The walls as anchored to the foundation do
not support a significant weight from above, but the structure has to resist lateral
forces due to wind and rainstorms. Dome construction was a two-person job, but
it was easily managed. The center height of the dome and walls is 82-in. (2-m),
requiring several ladders and two people to assemble. Indoor/outdoor carpet
installation completed the floor, which I wanted to both cushion my feet and
cushion the accidental impact of any dropped eyepieces. I hired a carpet installer
for this small 32-ft2 (2.9-m2) job but had to purchase a minimum amount of
carpet from the manufacturer.
A certified electrician utilized available breakers in my house electrical panel
and extended electrical runs 150-ft (45-m) in buried conduit to my observatory,
giving me a separate three-breaker panel in the dome. One hundred ten-volt
power cables were placed in one PVC conduit, and signal wires were placed in
another to avoid cross-talk as a potential source of noise. I had a light socket
wired into the wall of the dome so a red light could be installed, which preserves
night vision. Sound-suppression covers were installed over each of the two dome
rotation motors, and a hygrometer was installed, with a probe extending through
a small hole drilled in the observatory wall. A 30-day memory keeps a record of
inside and outside extremes in humidity and temperature. With the Meade
Superwedge in place atop the Astro Pier, my LX200 was set in place and the drive
base awaited connection to my Gateway desktop computer.
Creature comforts include an AM/FM/CD radio and a color television/VCR
and player. Listening to music from Carl Sagan’s Cosmos series might seem hokey
to some, but it certainly sets the mood when you are alone in the observatory,
under a starry night. Electrical interference is a possibility in a small, enclosed
location, so electrical equipment is divided and plugged into three separate
grounded sockets. I use a Belkin APC Battery Backup that is rated at 650 VA. It
provides adequate surge protection, eight back-up outlets, RJ-11 ports, and
video/telephone line protection.
A few words about lightning protection are in order. You must remember that
lightning is not only an electrical charge with a magnetic component but it is also
a plasma. It can jump to and from nongrounded to grounded objects at will. The
type of soil your observatory sits on plays the biggest part in good lightning protection. It is best to put the protection (i.e., lightning rods) away from the structure that you are trying to protect. The electricity coming into the observatory
through PVC conduit is itself routed through insulated flex tube, and each of
three receptacles in the observatory are GFI protected. The observatory is
grounded to Earth at two locations around the perimeter. To avoid equipment
damage through any electrical ground, I unplug all of the interconnecting cables
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CCD Astrophotography: High Quality Imaging from the Suburbs
and electrical equipment when not in use. A direct lightning strike in my backyard in 2004 could not have been better prepared for, but there is no design or
surge protection equipment that can protect from a direct strike. A typical lightning strike contains 1 billion volts and contains between 10,000 and 200,000 a of
current. I lost my LX200 mother board, RS-232 port, and a serial port on my computer. As a result of this expensive learning experience, the electrical equipment
remains unplugged in my observatory when not in use.
Meade Instrument Corporation was contacted after my lightning strike and
their company policy requires the entire telescope to be returned for repair. I did
not want to ship the almost 90-lb. (40 kg) telescope (in its shipping container)
to California from Florida, so I sought the advice of some colleagues on the
MAPUG and LX200 Internet groups for an alternative solution. Tim Prowten at
TelescopeService.com can repair most electronic problems with the LX200 telescope. When the components are returned, he gives you a full description of the
problems found, the repair that was carried out, and documents the final test to
ensure complete functionality. Whenever possible, you can send the electronics
only, not the whole scope. There are some things Tim will not do, namely replace
components that are the intellectual property (IP) of Meade Instrument
Corporation. These include the CNGC Library chips. If Tim finds a problem with
these parts, he will inform you before repairing anything else. Tim provides disassembly instructions and packaging instructions and contacts you when your
package arrives in good order. I spent a little over $125 (68£) and had my LX200
up and running within 5 business days of my damaged parts being shipped to
Tim.
E. Computer and Cables
I chose a Gateway Pentium 4 desktop PC running Windows XP home edition as
my observatory computer (see Fig. 2.17). The observatory is watertight, and
although the humidity and temperature can rise during a prolonged, hot summer
day, a hygrometer with memory that I installed inside the dome rarely recorded
temperatures exceeding 95°F (35°C) and 80% humidity. These extremes are
within the design capabilities of the electronics of the computer. The processor is
a fast 2.6-GHz Pentium 4 and the 40-GB hard drive has adequate temporary
storage for image files. I eventually transfer all files to CD-R disks, which is
explained in a later section.
An RS-232 cable connects the LX200 drive base to the computer, which allows
communication between my observing program (TheSky version 5, Level 4;
Software Bisque, Inc.) and the telescope. A floating cross-hair display on the computer’s virtual sky allows point-and-click slewing of the telescope to any target in
the evening sky. I use a USB hub to connect a Philips ToUcam Pro PCV740K camcorder and an SBIG STV camera. There are no hardware conflicts at all.
Communication between my observatory PC and my home office PC is established via an Ethernet cable network. My host operating system is Windows ME,
and again there are no conflicts. I ran Cat 5e cable over a 150-ft (45-m) distance,
buried in PVC conduit 9-in. (23-cm) in the ground. I do not have a frost line to
Equipment Inventory
Figure 2.17. Gateway Pentium 4 computer, 15-in. (38-cm) monitor, and television
monitor. Monitors and CD/radio are located in a recessed cubbyhole, so floor space
remains uncluttered.
33
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CCD Astrophotography: High Quality Imaging from the Suburbs
contend with, but the variety of palm trees that are planted on my property have
mature, spreading surface roots, so I wanted to stay below their reach. The
Ethernet cable runs in a separate conduit from the electrical cable, about 6-in.
(15-cm) apart. I use a Netgear® four-port hub (Netgear®, Inc.). When the panel
bulbs lit green for the first time, indicating an intact physical network, I was
thrilled!
F. Software for Observing and
Telescope Control
I purchased TheSky version 5 Level 4 (Software Bisque, Inc.) for my observing
routine, which is considered one of the premiere pieces of software to own for
observing and planning an evening under the stars. TheSky allows the user to
display a virtual night sky on the PC desktop, and the viewer’s location can be
customized to include the local horizon and physical obstacles (i.e., trees, buildings). The LX200 can be fully controlled, as well as the ability to print star charts
and watch time-lapse events such as eclipses, and updated TLEs (two-line elements) for satellites can easily be downloaded to command the telescope to find
these targets. These are the same TLEs that are used by NASA and NORAD.
Ephemeris positions for asteroids and comets can be downloaded from several
Internet websites so that these deep sky objects can similarly be tracked and
imaged with a telescope.
TheSky displays real-time cross-hairs on the computer screen to show exactly
where the telescope is pointing (see Fig. 2.18). Many telescope functions are available, including slewing, jogging, centering, or focusing a star.
I found a great freeware utility called RealVNC viewer, which allows my home
computer to take control of my observatory PC. RealVNC is a UK company
founded in 2002 by a team from the world-leading AT&T Laboratories in
Cambridge. RealVNC (Virtual Network Computing) software makes it possible to
view and fully interact with one computer from any other computer or mobile
device anywhere on the Internet. RealVNC software is cross-platform, allowing
remote control between different types of computers. For ultimate simplicity,
there is even a Java (a programming language designed for use on the Internet)
viewer, so that any desktop can be controlled remotely from within a browser
without having to install software.
I can run the telescope and CCD camera from my house, comfortable in the air
conditioning and not have to battle the mosquitoes. I have a manual filter holder,
however, which necessitates going outside to change filters. My wife is not quite
ready to grant me this last bit of automation by allowing me to purchase a motorized filter wheel: “You can walk to the observatory for free” she reminds me.
The observatory PC is set up as the host and the office PC is set up as the client.
Once installed, which was effortless, RealVNC is opened on the host computer
and then subsequently opened on the client PC. A successful link displays the
desktop of the observatory PC on the office PC desktop, virtually in real time. If
TheSky is opened on the observatory PC, or the STV camera/guiding console
Equipment Inventory
35
Figure 2.18. TheSky version 5, Level 4 screen capture. Rectangles depict FOV for various
configurations with the LX200 and Stellarvue refractor. The gray circle for the Rosette
Nebula denotes the approximate filamentous extensions of the nebula. (Used with permission,
Software Bisque, Inc.)
(STV Remote) is opened, the software is controlled from inside the house.
Pointing and clicking anywhere on the virtual sky commands the telescope to
move. Guiding parameters from the STV Remote console can be monitored and
changed from inside. I can safely make small moves and slew to new targets; I can
use the mouse to control the JMI focuser if the focus position changes during the
night. There are several out-of-bound positions of the telescope where it might
hit the mount, depending on the length of the imaging train, so movements are
small and at slow speed. I installed a wireless video camera mounted on the
observatory wall to monitor telescope slews from my home office.
G. Software for Image Processing
Astroart 2.0 (MSB Software, Inc.) was my first purchase for both image acquisition and preliminary image processing. There are many software utilities and
suites from which to choose. The two gold standards (Maxim DL, Diffraction
Limited and Adobe Photoshop; Adobe Systems) demand a higher level of understanding and skill and the willingness to fork over several hundred dollars.
36
CCD Astrophotography: High Quality Imaging from the Suburbs
Astroart, since upgraded to version 3.0, provides a beginner like me with a fully
functional and fairly user-friendly camera control and image processing
program. One improvement in version 3.0 is the ability to fully process in 32-bit
floating-point math. The software fully supports 32-bit flexible image transport
system (FITS) images. This means that key parts of an image, which are combined as a straight addition, are not necessarily saturated due to pixel values
reaching 65,534 analog-to-digital units (ADUs) (images reaching higher SNRs).
Astroart supports several file formats including the industry standard FITS
format as well as Joint Photographic Expert Group (JPEG) and bit-map graphic
format (BMP). Numerous functions, including image editing, image analysis,
various math functions, processing filters, and photometry and astrometry are
available. Four new algorithms (one star, two stars, planet, and correlation)
permit alignment and addition of every kind of image. The astrometric and
photometric calibration is a main feature of Astroart. It is carried out with an
integrated star atlas (18 million stars, up to 15th magnitude based on the Guide
Star Catalog (GSC). With just a few mouse clicks, it is possible to assign the
reference stars of the image for the subsequent reduction. Many amateur
astronomers use Astroart for photometry and astrometry on comets, minor
planets and super novae. After measuring the R.A., declination (Dec.) and magnitude of a minor planet or comet, Astroart automatically creates a correctly
formatted report from your measurements that can be sent to the Minor Planet
Center (MPC).
The Handbook of Astronomical Image Processing (HAIP) and its integral AIP
for Windows (AIP4WIN) processing software (Willmann-Bell, Inc.) is a second
program that I use for certain parts of my processing routine and is covered in a
later chapter (see Fig. 2.19). The software comes with a several-hundred-page
hard-cover textbook that is a thorough discussion of the theory and math
behind image processing. Several image processing tutorials are included on a
CD-ROM.
H. SBIG STV Camera and
Autoguider
The STV camera (Santa Barbara Instrument Group, SBIG) is a sensitive, cooled,
digital video camera that can autoguide and image without the need for a computer (see Fig. 2.20). Why autoguide? The longest unguided exposure that you
can take varies with the declination of the object being imaged, and the closer to
the celestial equator, the greater the drift that results from a less-than-perfect
polar alignment. Autoguiding helps level the playing field by directing the telescope and mount to track a guide star as it moves, monitoring and adjusting your
mount during an imaging session. It has been called a hybrid design because of
its dual functionality. SBIG is a recognized industry leader and the STV unit is
regarded as a premium autoguider. The STV uses a TC 237 CCD chip with 656 ×
480 pixels and has various binning modes. The single-stage thermoelectric
cooling can effectively take the camera down –25°C (–13°F) from ambient.
Equipment Inventory
Figure 2.19. AIP4WIN screen capture. During a multi-image processing session, the
software saves all image steps in a Data Log for subsequent review. (Used with permission,
Wilmann-Bell, Inc.)
Figure 2.20. STV Deluxe camera and control box. (Used with permission, Santa Barbara
Instrument Group, Inc.)
37
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CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 2.21. SBIG STV camera head attached to Celestron f/6.3 focal reducer and field
flattener, followed by JMI NGF-S focuser and Meade LX200. The reducer allows guiding
through the LX200 at a manageable 1575-mm effective focal length. (Used with permission,
Santa Barbara Instrument Group, Celestron, Inc., Jim’s Mobile, Inc, and Meade Instruments, Inc.,
respectively).
Exposures from 1/1000 s to 600 s are possible. Two major components are the
camera head [1 lb (0.4 kg)] and a control box (see Fig. 2.21). The camera nosepiece fits a standard 1.25-in. (3.2-cm) focuser. The STV control box is mounted to
a pier shelf, which was custom-made by Greg Mueller (Mueller’s Atomics) (see
Figs. 2.22 and 2.23).
The video output is seen on a built-in 5-in. (13-cm) LCD screen of the unit or
can be cabled to a video monitor (I use a television monitor on the auxiliary
setting) (see Fig. 2.24). The LCD monitor provides an image of the guide star as
well as a real-time graph of the last several minutes of guiding corrections in both
axes. I use the STV primarily as an autoguider, with calibrate and track modes. As
a stand-alone video camera, it will store 2 Mbytes of digital images in its onboard memory just like a digital camera. The images can be downloaded to a
computer at a later time or downloaded after each image is obtained if the STV is
directly connected to a PC at the time of imaging (see Fig. 2.25).
The STV automatically calculates exposure time and estimates the amount of
move to make, moves the mount in each of four directions, and measures the
results. The STV marks as many stars (up to eight) that it can detect. Calibration
Equipment Inventory
Figure 2.22. SBIG STV Deluxe camera control box mounted on pier shelf. Meade
Superwedge is above, and three-breaker panel is below the STV display box. (Used with
permission, Santa Barbara Instruments Group and Meade Instruments, respectively).
39
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CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 2.23. Greg Mueller (Mueller’s Atomics) fabricated an SBIG STV control box
bracket that allows the unit to fit nicely between the Meade Superwedge above and the
circuit breaker panel below. White switch box controls a red bulb in the observatory, which
preserves night vision.
Equipment Inventory
41
Figure 2.24. STV Deluxe video output can be viewed on built-in 5-in. LCD screen or on a
television monitor via video cable. (Used with permission, Santa Barbara Instruments
Group).
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CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 2.25. STV Deluxe screen capture. Using STV Remote version 2.0 software, an
image of the moon has been captured and downloaded to the observatory computer, where
it can be saved and further processed. (Used with permission, Santa Barbara Instruments
Group).
is the process whereby the STV camera learns how much and in what direction it
should move the telescope to correct for drift of a guide star that it is tracking.
During tracking, in Auto mode, the STV will find a suitable guide star after a
successful calibration, setting the proper exposure time. You can override Auto
by selecting Manual mode and adjust all guiding parameters.
When imaging through the piggybacked refractor, I guide through the LX200
with a Meade 3.3 focal reducer in place, which effectively reduces the focal length
to a less demanding 833-mm and a pixel scale of 3.4 arc-second/pixel. I typically
guide 5–15-min subexposures for extended targets without any major tracking
issues.
When I swap the camera for the guider, I guide through the refractor and
image through the LX200. This is the more challenging setup of the two because
the image scale increases and it is more demanding to image at higher resolution.
The seeing conditions rarely allow imaging at f/10 (2500-mm focal length); I
usually attach a 6.3 focal reducer and image at 1575-mm.
Equipment Inventory
43
I. Accessories
Meade Instruments Corporation had a great introductory offer when I purchased
my telescope a few years ago: a complete Series 4000 Plössl eyepiece set for $99.00
(53£). The range of eyepieces included 6.2-mm through 32-mm, and I additionally purchased a 24.5-mm super wide-field eyepiece and a Series 4000 8–24-mm
zoom eyepiece. These high-quality eyepieces are associated with low astigmatism
and off-axis color and provide high contrast and sharpness. Each eyepiece has a
soft rubber eye guard for maximizing comfort. The zoom eyepiece has smooth
movement and maintains optical collimation at all settings. Plössl eyepieces are
very popular for amateurs. The edge of field sharpness across the entire range of
focal lengths is well known.
A Barlow lens is an eyepiece amplifier. It effectively doubles the magnification
of the eyepiece and doubles the focal length of your system. I have a 2× shorty
(Parks Optical, Inc.) and an off-brand 3× Barlow. Barlow lenses are great for
improving planetary views and lunar views when seeing conditions support the
higher magnification. A Barlow lens can be placed between a star diagonal and
eyepiece to yield 2× magnification, and between a star diagonal and focuser to
achieve nearly 3× magnification.
100
Transmission in %
80
60
40
20
0
400 450 500 550 600 650 700 750 800 850 900 950 1000 1050
Wellenlänge in nm
Figure 2.26. Astronomik Ha filter, 13-nm bandpass. The red lines are the most important
lines from artificial light pollution. The green lines are the most prominent emission lines for
nebulas. The gray curve is the human eye´s night sensitivity. The blue line is the transmission
curve of the filter at 656 nm bandpass. (Used with permission, Gerd Neumann, Jr.’s
Astronomik, Inc.)
CCD Astrophotography: High Quality Imaging from the Suburbs
44
Various filters are used for visual use or imaging use. An ND-96 moon filter
(Meade Instrument Corporation) is used for contrast enhancement and reduction
of moon glare. A Lumicon Deep Sky Filter (Lumicon, Inc.) is used as a lightpollution-suppression filter, and narrow-band imaging is through a Lumicon
OIII (Lumicon, Inc.) or Astronomik 13-nm Ha filter (Astronomik, Inc.). (see
Fig. 2.26). A complete set of Astronomik Type II IR blocked LRGB filters
(Astronomik, Inc.) are my main imaging filters (see Fig. 2.27.) These filters are
optimized for CCD astroimaging and are 1.25-in. (3.2-cm) in size. All four filters
are used with a manual Astronomik filter drawer (Astronomik, Inc.) (see Fig.
2.28). The filter drawer, precision machined to maintain parfocal distances, holds
1.25-in. (3.2-cm) filters and is made of aluminum and brass. All parts are black
anodized and all surfaces are blackened to prevent infrared reflection. Blocking
infrared is often desirable on refractors to reduce the star bloating due to chromatic shift (inability of all colors to be brought to the same focus point).
A Losmandy ring and dovetail set (Losmandy Astronomical Products, Inc.)
attach my piggybacked refractor to the LX200. A two dimensional (2-D) balance
system is used on a rail system attached to the underside of the LX200. Fifteenpound (6.8-kg) flat weights slide on rails and are used to balance the imaging
setup depending on configuration.
100
Transmission in %
80
60
40
20
0
350 400 450
500
550 600 650
700
750
800 850
900 950 1000 1050 1100
Wellenlänge in nm
Figure 2.27. The transmission curves of the Astronomik Type II RGB filters are optimized
for CCD astronomy. Continuum radiators like stars and galaxies as well as objects that
shine only in single lines (e.g., planetary nebulas) are reproduced in their true colors. Each
filter blocks infrared wavelengths. (Used with permission, Gerd Neumann, Jr.’s Astronomik, Inc.)
Equipment Inventory
45
Figure 2.28.
Crayford focuser at
top, followed by
Astronomik filter
drawer, Meade
Instruments adapter,
and Starlight Xpress
HX916 camera.
(Used with permission,
Stellarvue Telescopes,
Astronomik, and
Starlight Xpress,
respectively).
All eyepieces are kept in an aluminum Orion accessory case (Orion Telescopes
and Binoculars, Inc.), which has padded bins for eight standard 1.25-in. (3.2-cm)
eyepieces and room for additional sundry accessories (see Fig. 2.29). I keep
packets of silica gel in the case to help combat humidity in the dome.
A JMI NGF-S electric focuser (Jim’s Mobile, Inc.) can be controlled from a
hand paddle or from a computer when plugged into the drive base of the LX200.
The focuser is designed for fine-focus control and allows only 0.5-in. (1.3-cm) of
total travel of the focus tube. The motor provides a level of control from either a
hand paddle plugged directly into the focuser or from software such as TheSky
when the focuser is plugged directly into the LX200 mount.
A Kendrick dew heater and controller (Kendrick Astro Instruments, Inc.) are
used to keep the telescope glass dew-free. Dew will sneak up on you at night as
the temperature falls and moisture condenses on the lens optics. The humidity is
typically high most of the year in Miami, Florida. My dew heater gets turned on
most imaging sessions. I do not see any degradation of image due to use of the
heating elements. I use a heating element wrapped around the corrector plate of
the LX200 and wrapped around the objective of the Stellarvue refractor. The
Kendrick system does an excellent job of keeping the glass free of dew and moisture by providing a low-voltage heater coil. I use a Pyramid Model PS-9KX 12-V,
46
CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 2.29. Orion Telescopes and Binoculars case. Foam cutouts allow various telescope
eyepieces, filter boxes, and assorted imaging accessories to be conveniently located. (Used
with permission, Orion Telescopes and Binoculars, Inc.)
5-a regulated power supply (Pyramid, Inc.) to control the Kendrick controller,
which is attached by Velcro to the LX200 fork arm (see Figs. 2.30 and 2.31). The
Pyramid controller has electronic overload protection and short-circuit and
thermal protection.
A standard metal First Aid box is attached to my observatory wall and provides
spacious 10-in. × 10-in. × 4-in. (25-cm × 25-cm × 10-cm) of convenient storage for
various items that I want quick access to in an organized fashion. The hinged lid
doubles as a handy shelf to temporarily place something on when opened (see
Fig. 2.32).
A metal Hartmann focus mask (with three holes) (Kendrick Astro Instruments,
Inc.) fits over the end of the LX200 and can be used to refine the focus (see
Fig. 2.33). The out-of-focus image generated by each hole merges when the telescope is in focus. The device goes by two different names, with Hartmann mask
describing a mask with multiple holes and Scheiner disk describing a mask with
two holes. Two wooden dowels placed over the end of the optical tube assembly
(OTA) serve a similar function. I like the dowels better. A Meade metal blue dew
shield for the LX200 (Meade Instrument Corporation) does not see much use, as
the observatory walls and dome provide adequate protection of both telescopes
from stray/off-axis light. Depending on direction being imaged, if stray light is
Equipment Inventory
47
Figure 2.30. Pyramid 12-v controller (Pyramid, Inc.), which powers the Kendrick Astro
Instruments Dew Remover system. Dew Remover controller is seen at the upper left, with the
black rotary knob. Phillips ToUcam Pro PCVC740K camcorder is shown inserted in the
LX200 1.25-in. (3.2-cm) adapter. (Used with permission, Kendrick Astro Instruments, Inc. and
Koninklijke Philips Electronics N.V.)
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CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 2.31. Pyramid 12-v controller (Pyramid, Inc.), which powers the Kendrick Astro
Instruments Dew Remover system. An electrical outlet strip can be seen attached to Le Sueur
Astro Pier. (Used with permission, Le Sueur Manufacturing Co, Inc.)
Equipment Inventory
49
Figure 2.32. Accessory case mounted to observatory wall. Cover opens down and acts
like a shelf.
pronounced, I will use the shield and need to rebalance the imaging setup
because the dew shield weighs about 2 lbs (900 g).
I use a home-built aperture mask made of Baader Mylar that fits over the end
of my 10-in. (254-mm) LX200. The solar material allows safe viewing and imaging
of the sun. I spent about $20.00 (11£) on the material in order to fashion a fullaperture mask. Sunspots look reasonable as does the Sun’s surface granularity,
but this is not a prominence filter (everyone would love to be able to view solar
prominences if these filters were not so expensive!), so I do not spend much time
solar observing.
A Series 4000 corded 9-mm (0.4-in.) reticle (Meade Instrument Corporation) is
used for refining polar alignment. Micrometric x-y positioning controls facilitate
locking onto a guide star, and the reticle pattern (double crossline with two concentric circles) can be placed anywhere in the field. The brightness control and
pulse control of the light can be adjusted.
I use a Meade 3.3 focal reducer/field flattener (Meade Instrument
Corporation) and a Celestron 6.3 reducer/field flattener (Celestron, Inc.). Both
accessories convert a native LX200 f/10 or Stellarvue f/6 telescope to a faster
imaging platform. This accessory makes it possible to have a dual focal ratio
instrument, without sacrificing image quality. It offers wide FOVs with any
Schmidt–Cassegrain telescope. Used for astrophotography, it reduces exposure
50
CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 2.33. Hartmann mask on the Meade LX200. A Hartmann mask with three holes is
a focusing aide. See text for explanation. (Used with permission, Kendrick Astro Instruments, Inc.)
Equipment Inventory
51
time by a factor of 3. Focal reducers are the opposite of a Barlow lens, shortening
the telescope’s focal length and reducing the magnification. Most reducers suffer
some form of vignetting when used with an SCT: The FOV gets cut off at the
edges, which can be corrected by using flat fields (discussed in Chapters III and
IV).
I keep a small vacuum cleaner in the observatory (I am a neat freak!) and use
carpet fresh deodorizer with baking soda a few times a year. Ant bait traps are
spread around the perimeter of the dome base and are changed every few
months. There is only so much you can do to thwart minor infestations, however.
Because the dome is not 100% impervious to the outside elements, once in a
while a wasp takes up refuge on the ceiling and I have a rude awakening when I
open the dome after a prolonged absence to find that an entire nest has formed.
J. ToUcam Camcorder
The ToUcam Pro PCVC740K camcorder (Philips, Inc.) is one of many popular
camcorders that has revolutionized the ability to capture magnificent images of
solar system objects (planets, Moon, Sun) and, with camera modifications,
extended deep space objects. For less than $100.00 (54£) out of the box, this
camera can easily be attached to a telescope (in place of an eyepiece) and wonderful images can be downloaded and displayed on a PC monitor in real time. The
CCD chip is 640 × 480 pixels and produces satisfying results at 5–10 frames per
second. The camera weighs a mere 100 g (4 oz.) and is powered via a USB cable.
Camera adjustment parameters include frame rate, contrast, gamma, brightness,
white balance, exposure control, and backlight compensation.
I like to take 45–60 s worth of images with the ToUcam attached to my LX200
typically with a 2× or 3× Barlow lens [effective focal length of 5000 or 7500-mm
(197-in. or 295-in.) respectively]. If the seeing conditions permit, the number of
frames that capture good detail can be numerous. Software packages can stack
these frames to produce a smooth and detailed image.
There is an entire online community (QCUIAG, Quickcam and
Unconventional Imaging Astronomy Group) devoted to discussing these
cameras, as well as video surveillance and digital cameras. Modifying these
cameras so that they perform much like a dedicated cooled CCD camera has a
large and popular following in the astroimaging community.
I use the software that came with the camera in order to capture images, but
another popular capture and initial processing program is Peter Katreniak’s
K3CCD Tools program. Video is memory-intensive. Each second of captured
Audio Video Interleave (AVI) file is approximately 1 MB in size, so a hard drive
can fill up quickly.
One neat feature of using a camcorder and the telescope is the sweeping vistas
of the Moon that can be viewed in real time. Using the LX200 keypad, the surface
of the Moon can be panned over as if you are in orbit, looking for a favorable
landing site! A future cable run from my observatory will allow me to download
the images to a wide-screen high definition television (HDTV) in the family
room, which should give an impressive view of the Moon and planets in real time.
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CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 2.34. Registax version 2.1.13 screen capture. Single frame of a 300 frame AVI
file, showing Moon crater Plato and selection box with crosshairs. All frames will be aligned
and stacked, based on various quality parameters that the user can define. (Used with
permission, Cor Berrevoets’ RegiStax Version 2.1.13 Beta.)
Cor Berrevoets and his development team are the software authors of the
famous RegiStax program, which is now in its third version as of January 2005.
This freeware allows hundreds of frames of an AVI film, downloaded from a camcorder, for example, to be aligned and stacked utilizing a very user-friendly interface. Processing options and wavelet filters make this program a necessary
addition to your imaging and processing program (see Figs. 2.34 and 2.35).
I also installed a wireless black-and-white video surveillance camera and keep a
small monitor in my home office. When I am remotely operating an imaging
session, I like to see the interior of the observatory and visually confirm telescope
slews if the movement across the sky is extended. I also like to monitor the
telescope during a slew to prevent any potential cable wrap. When doing a large
slew or when imaging near the zenith, the camera swings very close to the
Superwedge, so I like to monitor this.
Equipment Inventory
Figure 2.35. Registax version 2.1.13 screen capture. Aligned and stacked AVI file of
Moon crater Plato. Image can be resampled and saved in several formats for subsequent
processing. (Used with permission, Cor Berrevoets’ RegiStax Version 2.1.13 Beta.)
53
CHAPTER THREE
A Night of
Imaging Under
the Stars
(and Clouds)
One of the great things about having all of my imaging equipment securely
housed in an observatory is the quick setup routine to power-up and powerdown for the evening. When the weather changes in a heartbeat, it is less of a
physical drain to call it a night and close up shop. When the weatherman fails to
accurately forecast the night’s weather and the clouds part above my backyard, it
is just as easy to turn the key and open the observatory for the evening. I can set
up in less than 10 min and close up in less than 5 min.
I do an accurate polar alignment at least twice a year. My pier is not subject to
any movement due to frost lines or soil shifts, but I do a drift alignment in order
to eliminate any declination drift. Drift alignment is a technique used to get the
polar axis of your telescope parallel with the polar axis of the Earth. It is done by
watching selected stars “drift” in declination while viewing them. For an easy-tounderstand approach, see Chuck Vaughn’s treatment referenced in Chapter VIII.
From the type of declination drift, we can determine which way our scope is misaligned and can correct it accordingly. Thus, the name “drift align.”
During the work week, I keep track of my local weather with a live radar
Doppler loop feed, displayed on my computer with a Java applet. Many local television news agencies in the United States that have an Internet site have a local
online forecast, updated several times during the day, if not a direct link to live
Doppler radar. Another great Internet site used for planning is the Clear Sky
Clock at www.cleardarksky.com. At a glance, it shows when it will be cloudy or
clear for up to the next 2 days. It is a prediction of when your site and the surrounding 10 miles (17 km) will have good weather for astronomical observing.
The forecast data comes from the Canadian Meteorological Center, which is
unique because the forecasts are specifically designed for astronomers. There are
clocks for 2292 locations.
55
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CCD Astrophotography: High Quality Imaging from the Suburbs
What conditions make for a good or great night of imaging? Two items come to
mind. First, equipment needs to be optimized. It is important to match the telescope’s focal ratio to the camera in order to maximize resolving power of the
CCD-telescope combination. Nyquist sampling theory requires two pixels for
each unit of resolving power. For example, if your telescope/camera can resolve
1 arc-second/pixel, you should ideally choose a configuration that ensures two
pixels per arc-second in order to maximize the resolution. Binning refers to the
ability to combine pixels. A CCD chip is an array of rectangular light detecting
regions (pixels). Sometimes images can be taken by combining the information in
adjacent pixels and make them one effective superpixel. The advantage of
binning is that there is a reduction in noise and the camera sensitivity is
improved, both at the cost of lower resolution. When one pixel in the camera
maps to one pixel in the image, the camera is said to be at its highest resolution.
Image scale describes how much sky each pixel covers. Imaging conditions will
impact the theoretical limit of your equipment’s resolution on any given night.
My Stellarvue refractor and HX916 camera image with a resolution of just less
than 2.8 arc-seconds/pixel. The LX200 reduced to 1575 mm (62 in.) focal length
and HX916 camera image with a resolution less than 1 arc-second/pixel; this is
very difficult to do given my imaging conditions. The weather is the second determinant that impacts a good night of imaging. A few weather-related terms as they
are used in astronomy should be discussed. Cloud cover is obvious and refers to
total cloud cover over an extended area. Local forecasts might miss low clouds
and afternoon thunderstorms however. Transparency refers to the total transparency of the atmosphere from ground to space and is calculated from the total
amount of water vapor in the air. Above-average transparency is necessary for
good observation of low-contrast objects like galaxies and nebulae. Deep sky
imaging is best done on nights of high atmospheric transparency. Cold fronts
that move through your area usually help by bringing in cold, dry, clean air and
washing out pollutants and dust. However, open star clusters and planetary
nebulae are quite observable in below-average transparency. Large globular star
clusters and planets can be observed in poor transparency.
Excellent seeing means that at high magnification you will see fine detail on
planets. In bad seeing, planets might look fuzzy and lack detail at any
magnification, but the view of galaxies and open star clusters is probably undiminished. Bad seeing is caused by turbulence combined with temperature differences in the atmosphere. Daytime heating contributes to nighttime seeing,
especially if you image over a large concrete or asphalt area. Some people observe
worse seeing though their telescope than what a perfect seeing forecast would
predict because of tube currents.
Darkness is not a weather term but it tells you when the sky will be dark,
assuming no light pollution and a clear sky. It takes into account the Sun’s and
Moon’s position, moon phase, and solar cycle. It does not consider light pollution, dust, clouds, snow cover or the observer’s visual acuity. Thus, your actual
limiting magnitude might be different.
Some imagers need to know about wind speed. The wind forecast will not necessarily determine whether or not you can observe, but it will probably affect
your ability to image. In particular, long-focal-length astrophotography or
observing with large dobsonians require light wind conditions. Large dew shields,
A Night of Imaging Under the Stars (and Clouds)
57
which act like sails, might be impossible to use in windy conditions. Having a
telescope protected by observatory walls allows for imaging in otherwise poor
conditions due to light winds and can help block out line-of-sight stray light
(glare).
Humidity variations will not determine whether you can observe, but it might
affect observer comfort and can indicate the likelihood of dewing. However,
dewing is not simply correlated to relative humidity. Dewing tends to happen
when the sky is clear, the temperature is dropping, and there is not much wind. A
forecast of 95% humidity under a darkening sky is a pretty good clue that the
dome should remain closed: It is about to rain!
Temperature near the ground is often reported. Although temperature variations will not determine if you can observe, the forecast can be handy for choosing clothing for cold observing conditions. Observers with thick primary mirrors
should take note of falling temperature conditions because their mirrors might
require additional cooling to reach equilibrium and thus prevent tube currents.
It is a short walk to the observatory. I turn a key and throw a toggle switch, and
the electric shutter opens. A wall-mounted hygrometer tells me that the current
temperature inside the observatory is within a few degrees of outside temperature, so it does not take long for all of the equipment to reach thermoequilibrium
(usually within 15–20 min). My Gateway desktop computer is already on and in
hibernate mode, so after “waking up,” I confirm that the local network is intact
and then plug in the CCD camera and STV autoguider unit. I turn on the
Kendrick dew heater, which keeps the LX200 corrector plate and refractor objective glass free of dew. Some nights I image unguided if integrations are less than
180 s, but I set up the autoguider nevertheless, because the camera will be nice
and chilled should I decide to image with extended integrations. Finally, I turn on
the LX200 and hear the familiar “beep.” The initialize routine on the LX200
paddle (version 3.4 firmware) is effortless for a permanently mounted telescope.
The hand-paddle menu will have a checkmark next to Polar Mode and all you
have to do is hit ENTER.
With the computer on, I open the various programs that I will use on the
observatory desktop. TheSky (Software Bisque, Inc.) is my planetarium and telescope-control software. I select a bright star in the sky (during twilight) that I can
visually see and can identify, place the mouse cursor on the same star in the
virtual sky, and synchronize on it. Now, the telescope and computer are synchronized in terms of location. I use a freeware program called Atomic Clock Sync
(v2.6) (www.worldtimeserver.com) to synchronize my PC clock with a time
server. When I update the time clock in TheSky, the signal updates the LX200
hand paddle and now the telescope, PC, and software are all synchronized.
I load the freeware program RealVNC Viewer, which makes it possible to view
and fully interact with one computer from any other computer on the local
network. My office desktop PC, 150 ft (45 m) away, can control the telescope and
any opened software program on the observatory PC desktop. The observatory
PC acts as the host and the office PC is the client. I also open Astroart 3.0 to
control the camera and STV Remote to control/monitor the autoguider.
The STV autoguider must be initialized with the correct time and date, and you
must verify that the telescope parameters are correct (aperture, focal length, type
of telescope you are guiding through, etc). I usually guide with a Meade 3.3 focal
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CCD Astrophotography: High Quality Imaging from the Suburbs
reducer or a Celestron 6.3 focal reducer. The effective focal length becomes
825 mm (32 in.) and 1575 mm (62 in.), respectively, from a native 2500 mm
(98 in.) at f/10.
The STV autoguider takes exposures of a small part of the sky. A guide star is
chosen, and after each exposure in two positions along each axis, guiding software measures the drift of the star and directs the mount to move in order to
return the star to the same starting location. The STV can make measurements as
accurate as 1/30 of a pixel. The precision that is required for successful guiding is
measured in arc-seconds, or 1/3600 of a degree. The R.A. axis is always moving
during a guided exposure, and the autoguider tries to keep up with the apparent
motion of the slowly rotating Earth. The declination axis is stationary unless a
correction is made.
I manually slew the telescope while looking through the 8 × 50-mm finder
scope until I spot a relatively bright star. Because I am synchronized with TheSky,
I could also point and click with the mouse on the virtual sky and slew to a star.
My LX200 GOTO accuracy is fairly good in most parts of the sky, so I would come
close to the intended target if using TheSky. Either way works fine. The finder
scope, piggybacked Stellarvue refractor, and LX200 are optically aligned along the
same axis, so the guide star is also visible on the LCD screen of the STV. I go
through the Calibrate routine in the STV to ensure that the LX200 mount properly tracks along all four axes. When each axis receives a “Pass” message, you are
ready to Track. Calibration allows the STV camera control software to model the
LX200’s behavior during guiding corrections. Some imagers recalibrate when
declination changes by 10° or more or when imaging in a part of the sky very different from where the initial calibration took place.
I own a manual Astronomik filter holder (Astronomik, Inc.), which attaches
between the telescope and camera. Whether I am imaging in monochrome or
contemplating trichrome color imaging, my Astronomik filter set is almost parfocal and very little focus adjustment is necessary if I need to change filters during
an evening’s imaging session. Whether you can afford a more expensive motorized filter wheel or a more affordable filter holder, the requirement is the same:
You do not want to touch the telescope or change the camera orientation in any
way.
Astroart 3.0 is initialized and the first order of business is to go through the
focus routine, which is iterative. Although a star is a point source, you cannot
shrink a star’s image to a point regardless of how perfect your focus is. The
sequence is straightforward. I take a short exposure of a star (simultaneously
present on the STV LCD screen and in the finder scope), and after it is downloaded to the desktop (11 s when binning 1×1, approximately 3 s when binning
2×2), I draw a selection box around the star. The size of the selection box is sensitive and will determine whether you see a scintillating star within a small focus
box (see Fig. 3.1), in real-time on your desktop, or whether you see random noise
(see Fig. 3.2). Typical settings for the focus routine are 0.3-s integrations,
unbinned 1×1. Fabio Cavicchio at MSB Software, Inc. suggests that the focus box
need not be constrained in size, but in practice, any box larger than 30+ pixels on
a side does not initialize the focusing routine.
I manually tweak the knob of the Crayford focuser on the Stellarvue refractor
(my JMI electric focuser is attached to the LX200) until the star pattern in the
A Night of Imaging Under the Stars (and Clouds)
59
focus window is a tight cluster of pixels. Stars do not focus to a true point, but
usually a small pixelated cross-pattern is attained. The idea is to get the FwhmX
and FwhmY values as small as possible and the total star count (expressed in ADU
values) as high as possible. Fwhm refers to full-width half-maximum, which
better reflects the approximate size of the star’s image as seen by the eye. It is the
width across a Gaussian profile of the star’s light when it drops to half of its peak,
or maximum, value. It is a simple and well-defined number that can be used to
compare the quality of images obtained under different observing conditions. On
a steady night of imaging, a magnitude 6 star typically yields both FwhmX and
FwhmY values under 1.5 with my setup. The better the focus, the brighter the
pixel values because the star light is concentrated into a tighter image area.
Atmospheric turbulence will scatter light and cause the star to dance around a
bit. I have two 0.0625-in.-diameter (1.5-mm) lengths of wire perpendicular to
each other just inside the threaded lip of my refractor dew shield. These wires
produce an artificial diffraction spike pattern by partially blocking the light and
this makes it easier to appreciate perfect focus during the focus routine. I lock
down the draw tube to keep the camera and filter holder at perfect focus. Take the
time to perfect your focusing routine: Nothing else that you do tonight will have
as dramatic effect on the quality of your images. Sitting down with your images,
Figure 3.1. Astroart 3.0 screen capture. Selection box has been drawn around a
magnitude 4 star, to the left of bright Procyon (magnitude 0.5). Diffraction spikes are
artificial. Focus window reveals good focus for image: FwhmX and FwhmY values are
unchanging and a Focus value of 1123 is maximum. (Used with permission, MSB Software, Inc.).
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CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 3.2. Astroart 3.0 screen capture. Selection box has been drawn around a star in
the Rosette Nebula. Diffraction spikes are artificial. Focus window reveals good focus for
image: FwhmX and FwhmY values are unchanging and a Focus value of 1708 is maximum,
but the focus window does not show star. This is a known bug with the software and the
Windows operating system. (Used with permission, MSB Software).
hours after acquiring them, only to find fuzzy donuts instead of crisp stars is an
eye-opening experience, not to be repeated.
Now the autoguider is calibrated; the camera is cooled and focused, the planetarium software, computer, and LX200 are time-synchronized, and the office PC
is client-enabled and can control the host PC in the observatory. There is only
one thing left to do: select a target to image! Ideally, target selection should be
made in advance of beginning your imaging session. As alluded to previously, it
is desirous to image a target as it is transiting or approaching culmination (i.e., its
highest point in the sky). Sometimes, depending on scheduling, I have no idea
what “is up” and I scan the local meridian for any objects that happen to be transiting at the particular time that I am imaging. I place the telescope mouse cursor
in TheSky on the local meridian and slew through safe declination limits of the
telescope, scanning the FOV display and looking for an interesting target (see
Fig. 3.3).
A target is selected and a test exposure is made. Individual frames should have
as long an integration as possible without saturating key parts of the image that
you are trying to make. In the real world, this will depend on the quality of your
mount without getting star trailing, how long you can go before skyglow domi-
A Night of Imaging Under the Stars (and Clouds)
61
Figure 3.3. TheSky version 5, Level 4 screen capture. Rectangle depicts FOV of Starlight
Xpress HX916 camera and Stellarvue® Nighthawk refractor, an impressive 49 × 62 arcminutes. The gray circles denote the approximate filamentous extensions of the nebulae.
Orientation of the field has been matched to camera orientation: note the N and E (for North
and East, respectively) in the upper left corner. (Used with permission, Software Bisque, Inc.)
nates the image, and so forth. I rotate the virtual sky’s FOV so North is up (and
East is to the left) and this matches my camera orientation, which is orthogonal
to the telescope’s R.A. and Dec. axes. I am looking at a few things when I shoot
my test exposure. First, I want to be able to see the object and not have it overwhelmed by background skyglow. I typically image anywhere from 120 to 600 s. If
an extended deep-space object is in a dense star field with bright stars, for aesthetic reasons I might plan ahead and take 30–60 s images in order to capture the
star field without having unacceptable star bloat or saturation. I then take deeper
integrations in order to record the extended object. Processing routines (discussed later) allow combining both integrations in order to showcase a pleasing
star field and deep extended object.
I engage the autoguider and hope that there is an adequate star in the field to
use as a guide. Sometimes this is the trickiest part of trying to begin an imaging
session. I can say from experience that this is where skyglow has an immediate
impact on an imaging session. Magnitude 6+ stars that are good to guide on are
sometimes unavailable in the field that is being imaged. The STV guider can be
tweaked by increasing the integration time of the camera, but the goal with my
LX200 mount is to guide with less than 2–4-s exposures, trying to get star ADU
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CCD Astrophotography: High Quality Imaging from the Suburbs
counts of less than 2500 units. The longer the integration used for guiding, the
greater the likelihood of recording a guide star at the expense of poor mount performance. A 1–3-s exposure is usually just right. Too short of an exposure and the
guider will be guiding more on seeing than on a star and be correcting all over
the place. Too long an integration and the mount might wander too much during
the exposure, and you will have large correction swings. The only rule of thumb is
“the shorter the better,” but depending on seeing, the value might change night to
night.
Aggressiveness on the autoguider can also be changed. A setting of 1 on the STV
means that the guider will make the full correction it calculates it needs to make.
So, if the guide star is 0.4 pixels off in R.A., for example, it will try to move
0.4 pixels with a setting of 1. The aggressiveness is balanced by the Max
Correction, which is the maximum pixel distance the STV will try to move the telescope for any one correction. So, if the STV determines that the guide star is
0.4 pixels off in R.A. but the Max Correction is set to 0.5, the calculated move will
be 0.2 pixels, and after another guide exposure, the remaining error might be corrected (as long as the mount does not add more error in the meantime!) You want
to keep oscillations to a minimum and produce less erratic and smoother corrections. The aggressiveness, Max Correction, and averaging of calculated movements before a correction is made can be adjusted in real time, so all is not lost if
guide exposure integration times cannot be held to less than approximately 2 s.
The Technical Innovations Home-Dome design of the 6-ft (1.83-m) dome does
not have a split front door. This means that the opened dome slot must be in the
home position in order to enter or exit the dome. The door and supporting dome
ring must be aligned in the home position for the door to open. This is fine if you
only want to image on the local meridian (R.A. = 0, any Dec. within the telescope’s safe slewing limits) or if you do not mind staying inside the dome during
an entire imaging session. Because my goal during most imaging sessions is to go
inside my house and monitor/control the session from my office computer, I
needed a way to get out of the dome. Jerry Smith at Technical Innovations helped
me modify the front door and latch system. I can now enter and exit the dome
regardless of the orientation of the dome slot and telescope (see Fig. 3.4).
When a test exposure is adequate, I sync the artificial telescope cursor in
TheSky with the target as it appears in the virtual sky. The Astroart 3.0 camera
control software allows for several items to be selected: exposure length, number
of exposures, binning mode, and a file name and directory location in which all
images will be saved.
I engage the IR detectors that are attached to the LX200 and piggybacked
refractor: These sensors keep track of the dome slot opening, and during an
extended imaging session, they automatically direct two dome motors to rotate
the dome counterclockwise in R.A., always keeping the dome slot opening in
front of the telescope. I engage the STV autoguider, begin the camera integrations, and exit the dome. On my office PC desktop, the STV autoguider window,
planetarium software, and camera control window are all available during the
remote imaging session. Figure 3.5 shows a RealVNC screen shot on my control
room computer, with the STVRemote program open on the desktop.
Noise, which shows up as graininess in an image, is approached with specialized imaging frames. In addition to light frames, other images need to be taken
A Night of Imaging Under the Stars (and Clouds)
63
Figure 3.4. Technical Innovations Home-Dome with a modified front door and latch
system. Entry and exit can take place regardless of the position of the dome slot. (Used with
permission).
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CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 3.5. RealVNC software screen capture on control room computer. An image of a
star (with selection box) has been captured by a Starlight Xpress HX916 camera and
downloaded to the observatory computer. The same star is being tracked by the STV
camera, and instantaneous X and Y pixel movements are shown in the window. AEX and
AEY values represent average moves made over the preceding 16 corrections, made in
both R.A and Dec., respectively. (Used with permission, Santa Barbara Instruments Group).
(in groups of 5–10, or more) that will be used during image processing. These
other types of image are bias frames, dark frames, and flat-field frames. When the
exposure time is close to zero (1 ms is the shortest exposure on my HX916), we
would expect pixel values to be close to zero-brightness. A bias frame represents
the pixel brightness values recorded by the CCD detector at almost zero exposure
time, with the lens cap on. It represents residual system noise that is always
present, regardless of the duration of an exposure. The noise is typically so low in
the bias frame that many imagers do not bother incorporating them in their data
reduction routine. If your dark frame and light frame images have the same exposure time, you do not have to take bias frames.
Dark frames represent the thermal noise present on the CCD chip when no
light strikes the CCD detector. Each dark frame represents reproducible noise on
a CCD chip for a specified integration time and temperature. The greater the
cooling in the camera, the lower the thermal noise. Dark frame images are taken
with the same integration time as a light frame. Thermal noise varies from image
to image, but if the temperature remains fairly constant, the dark frame will be
fairly consistent (see Fig. 3.6). Incorporating dark frames during image reduction
A Night of Imaging Under the Stars (and Clouds)
65
Figure 3.6. Astroart 3.0 screen capture. Dark frame image comparison. Dark frames 001
and 010 are each of 180-s duration, taken 32 min apart factoring in the 11-s USB
download time for each. The Starlight Xpress HX916 camera does a good job at keeping
the camera CCD chip cooled, as the average ADU count and standard deviation are in
good agreement. Observatory conditions at the time of exposure were 85°F (29°C) and
80% humidity. The master dark frame is a median combine of the 10 images. (Used with
permission, MSB Software, Inc.).
additionally eliminates cosmic ray hits. The idea is to subtract the dark frame
from the light frame in order to leave an accurate and clean record of the light
that the CCD detector recorded, eliminating artifacts such as hot pixels and
cosmic ray hits.
Flat-field frames are taken to record the variations in brightness, reflections,
and optical artifacts (dust motes, lint) located anywhere in the imaging train. The
visual impact of dust varies with its distance from the CCD chip (the focal plane).
Flat fields will help correct uneven backgrounds due to vignetting when a focal
reducer is used. To create the flat field, what you want to do is take an image of a
very evenly illuminated surface. This is not as easy as it might sound because an
evenly illuminated surface presenting itself square to the CCD chip’s surface is
required. Learn a technique, any technique, and you will appreciate the big difference in the appearance of your images. Flat-field techniques include stretching a
white tee-shirt over the telescope tube opening, taking an image of the sky at twilight (with hopefully none to few stars present), taking an image of a sky that is
clouded over, or using a light box. Regardless of the technique that you use, you
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CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 3.7. Dark frame-reduced (left) and dark- and flat-field-reduced (right) image of
spiral galaxy M65.
must not rotate the camera, change focus, add (or remove) a dew shield, or
change a filter. The focus position cannot change because the shadows created by
the dust motes will change in size on the image. You are trying to capture an
image of your optical system in the same arrangement as the light images were
taken. See Fig. 3.7 for an example of dark frame and flat-field image reduction on
spiral galaxy M65.
There are a few considerations to keep in mind. Flat fields are difficult to take
during a bright Moon or if there is a nearby bright light because of the resulting
gradient that will most certainly show up. Off-axis (oblique) lighting can also
cause problems because of the uneven illumination that will fall on the CCD chip.
A gradient that is created on your flat-field frames makes it more difficult to
process out, but it is not impossible. If you are doing trichrome imaging, the gradients that are created in a less-than-ideal flat and even background can cause
wild color variations among the red, green, and blue frames.
Building a light box will allow you to control the flat-field process (see Fig. 3.8).
No longer do you have to worry about extraneous or off-axis light. A light box is
constructed large enough to fit snuggly over the end of your telescope tube. There
are several plans available on the Internet to construct a sturdy, inexpensive box.
My box is made of foam board and clear plastic. I used a glue gun to attach the
sides of the box. Four incandescent white bulbs provide the internal illumination,
which is filtered through a sheet of drafter’s vellum (some people use milk
plastic) before illuminating the CCD chip. I use an AC/DC regulator and dimmer
switch so that I do not go through too many 9-V batteries. I use an integration
time so that ADU counts are roughly 40–60% of the CCD chip’s saturation level
(two-thirds well capacity for my HX916). For the HX916, I usually get counts of
26,000 to 40,000 ADU.
A Night of Imaging Under the Stars (and Clouds)
Figure 3.8. Light box for flat-field images, constructed of foamcore board and clear
plastic. The round circle just fits the dew shield of the Stellarvue refractor (80 mm). Black
and red switch for use with the AC/DC regulator is at the top of the box.
67
CHAPTER FOUR
Processing
Astrophotos
Made Simple
Well, let us cut to the chase: There really is nothing “simple” about processing
astrophotos. Oh, how I wish it were simple! The good news is that there are many
talented imagers out there who have paved the way for the likes of us newcomers.
If your favorite image processing software has a less-than reader-friendly manual,
there is a good chance that several people are online, on any of several Internet
groups, at any hour of the day, anywhere in the world, willing and eager to
answer your questions. Processing your images, however, is not a one-size-fits-all
endeavor. When I started image processing in early 2002, I was dismayed that
there was no single book, reference sheet, or manual that explained what to do, in
easy-to-understand language.
To be sure, there are lots of good books on the subject, lots of software to select
from to accomplish your goals, and plenty of knowledgeable and friendly imagers
out there willing to assist you. Like everything else in life, it takes some effort to
get good at something meaningful. Read and assimilate whatever you can get your
hands on and put what you learn to use during an image processing session by
practicing different techniques. This chapter is intended to describe in some detail
what is involved in image processing, from a beginner’s perspective. All one needs
to do is skim the several-hundred-page book by Ron Wodaski (The New CCD
Astronomy, The New Astronomy Press, 2002) to appreciate that my approach and
treatment of the subject merely glosses over the fundamentals. After reading this
chapter, you will not be magically transformed into a Robert Gendler, a Tony
Hallas, a David Malin, or a Dennis di Cicco. You might not be any further along
the learning curve. However, this is the approach that works for me after a few
years of trial and error. Hopefully, you might pick up a pearl or two.
The Internet makes it possible to quickly see the images of our colleagues
around the world. We can read about their setups and study their equipment,
69
70
CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 4.1. Astroart 3.0 screen capture. Single 180-s-integration raw dark frame. Range
of pixel values is 2176 to 64380, with the histogram showing the majority clustered at
around 3000 ADU counts. (Used with permission, MSB Software, Inc.)
compare image resolution, and get a hint of imaging sky conditions and local
weather. Many imagers are natural teachers: Their websites not only proudly
display their images, but many imagers are eager to share their processing skills
and techniques and invite others to email them with questions. “See one, do one,
teach one.”
The best CCD images have a good SNR. To get the highest possible ratio when
imaging under light-polluted skies, we should take the longest possible exposures
and combine multiple images. Image processing ultimately begins at the telescope, because proper planning involves taking critically focused light images
and matching dark frames, and taking flat-field images. Many images of longenough duration need to be available for stacking when you sit down to process
them in order to combine them into a high-quality image.
Thus, the imaging session has come to an end, and it is either late at night or
early the next morning. You have accumulated your raw images and matchingintegration dark frames (see Fig. 4.1), flat-field images (see Fig. 4.2) and their
matching dark frames, and bias frames (see Fig. 4.3) have been taken. If you are
doing trichrome imaging, each filter should ideally have a set of flats and matching darks for the flats. The first thing I do is transfer the contents of the folder
that all of the images are saved in to a folder on my office PC. I transfer across the
local network, which takes several minutes. I leave the computer in hibernate
Processing Astrophotos Made Simple
71
Figure 4.2. Astroart 3.0 screen capture. Single 0.5-s flat-field frame, raw image. Notice
the dark black corners at the bottom left and right of image. This represents optical
vignetting. A flat field will correct the same dark black corners of the image frames. (Used
with permission, MSB Software, Inc.)
mode and close down the observatory, covering the telescope and unplugging the
telescope and cameras. Depending on the time (and whether you have to work
the next day), there is now a folder of images sitting on the office computer’s hard
drive, ready to be processed. This folder contains the fruits of our labor, what we
worked so hard to obtain.
Image reduction (or calibration) refers to cleaning up your images in order to
reveal the wanted data in the best possible light (pun intended). We want to
correct defects in the image-taking process and remove some of the noise that is
random and unpredictable (variations in brightness levels among and between
multiple exposures), as well as some of the system noise, which is inherent in the
equipment. When the camera is cooled, for example, the CCD detector has less
noise and you will be closer to a higher-quality raw image. Like focusing, image
processing rewards begin with optimizing all conditions at the telescope. Noise
and unwanted artifacts that we can do something about include optical dust,
background noise (skyglow), and internal reflections in the optical train.
Calibration refers to what we need to do first, which is remove the noise from
our images. AIP4WIN software (Willmann-Bell, Inc.) is the first program that I
open. This software has a Calibrate routine which allows the master dark frames
and dark-frame corrected flat fields to be stored in a memory buffer. See Fig. 4.4
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CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 4.3. Astroart 3.0 screen capture. Single bias frame, 1-ms integration, telescope
capped. Notice that there are still pixel counts, ranging from 1954 to 3467, even with no
light hitting the CCD detector. (Used with permission, MSB Software, Inc.)
for a screen capture of AIP4Win’s Calibrate window. Let us say that I took 10
dark frames, each 300-s and unbinned 1×1 to match the 300-s unbinned 1×1 light
frames. I median combine all 10 dark frames and store the master dark frame in
memory. Next, I median combine all flat field images into a master flat-field,
median combine all flat-field dark frames, and subtract the master flat-field dark
from the master flat field. Bias frames are similarly median combined and saved
in the memory buffer. These images comprise a reduction group and will be
applied to the light frames, a process called image (or data) reduction, in order to
yield a pleasing image that reveals as much data as possible.
A few words about stacking/combining methods. There are four choices:
summing, average combining, median combining, and sigma combining.
Summing is not available in all software programs, usually for a good reason;
namely software that does not do the addition in floating-point math will saturate
the image once values go above 65,535 ADU counts. The information will be lost
and can never be recovered. Adding using 16-bit integers leads to this information loss. Astroart 3.0, which I also use for image processing, allows summing in
floating-point math. When averaging subexposures, the amount of signal in the
final image is equivalent to the length of just one subexposure. For example, 60,
1-min subexposures averaged are equivalent to a 1-min total exposure in terms of
the amount of actual signal (while noise is significantly reduced by the √[n],
Processing Astrophotos Made Simple
73
Figure 4.4. AIP4WIN screen capture. Advanced Calibration routine allows all reduction
group images (bias frames, dark frames, flat field, and flat-field dark frames) to be loaded
into AIP4WIN’s memory buffer. Multi-image processing can then begin. (Used with permission,
Wilmann-Bell, Inc.)
where [n] is the number of averaged subexposures). If you had added the subframes instead of averaging, then the total amount of signal in the combined
image would be the sum of all the subexposures. Adding 60, 1-min subexposures
will result in the amount of signal equivalent to a single 60-min exposure. The
main consideration, however, is not the total signal itself but rather the SNR.
Adding and averaging provide the best SNR and produce very similar results as
long as floating-point math is used.
Median combining is useful for stacking images that might have artifacts, such
as airplane or satellite trails or cosmic ray hits. Median combining is useful when
compositing many dark frames because pixel values that are high or low are canceled out, and the middle value of each pixel is assigned. Cosmic ray hits are eliminated. You have to have a minimum of three images to use this combination
method.
Ray Gralak’s Sigma pre-beta 11 freeware program (and Astroart 3.0’s Sigma
combine routine) provide a fourth way to combine images. The Sigma combine
routine further reduces noise in your images compared to using a simple
average/mean combine. Sigma has two algorithms to reduce noise when combining images. Images must be aligned and coregistered before using this program.
Darks and flats do not need to be registered nor should they. Also, the more
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CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 4.5. Sigma Combine Pre-beta 11 screen capture. Small area of Rosette Nebula
shown after combining 15 previously aligned and coregistered frames. No dark frames or
bias frames were applied. Image is smooth and free of any hot pixels or other artifacts.
(Used with permission, Ray Gralak’s Sigma Combine Pre-beta-11).
images you combine, the better Sigma will work. To truly see the best results, you
should combine at least 10 darks, flats, or light images (see Fig. 4.5).
AIP4WIN is still open on my desktop, and all of the master reduction group
images are stored in the memory buffer. I open the Multi-Image Processing
routine and select all of the light frame images (highlight the first image in the
folder, press SHIFT, and select the last image in the folder. All images will be
highlighted). The light frame images must be aligned, pixel for pixel, before
stacking to yield a higher-quality image. With the Align and Calibration buttons
bulleted, the light frames are loaded and two reference stars are selected on one
of the images to allow the software to align and coregister all of the images using
these two stars as a reference. Both AIP4WIN and Astroart 3.0 use two star centroids to shift and rotate images into alignment. When tracking with the STV
goes great, my mount still experiences a drift in declination and right ascension
of 5–10 pixels over a 2–3-h period. I attribute this drift to a less-than-perfect polar
alignment. When I image unguided, my drift is worse. The point is that software
brings things under control by allowing all elements of each image to nicely align
with each other.
I used to calibrate, align, and stack the result in AIP4WIN until I was introduced to the Sigma combine algorithm. Now, I calibrate and align the images in
Processing Astrophotos Made Simple
75
AIP4WIN, save the images to another folder that I name “Aligned,” and run these
images through Ray Gralak’s Sigma pre-beta 11. Actually, I review each image
before stacking to make sure that there are no outliers (i.e., trailed star or major
artifact). If so, the image is discarded.
The routine in the Sigma combine program can take several minutes to complete. Sixty images unbinned 1×1 are 1300 × 1030 pixels each. The combine
routine is memory-intensive even on my operating system (Windows-based,
2.6-GHz processor, 512 MB RAM). Once the stacking is done, the unfiltered
image is retained as a FITS image and opened in Astroart 3.0. Why three separate
imaging programs so far? Well, for me, each program has its strengths and weaknesses. Although Astroart 3.0 has incorporated a Sigma combine routine, for
example, the parameters for the combine algorithm cannot be changed, so I use
Gralak’s program. AIP4WIN has a greater ability to control the alignment and
coregister routine than Astroart 3.0. Astroart 3.0 has more intuitive controls for
image processing once an image is aligned and stacked. Again, after 3 years of
image processing, this is my educated opinion: “Your mileage may vary.”
Astroart 3.0 has an automatic screen stretch. When the Sigma combine image
is opened on the desktop, it is typically dark black with a few scattered white dots.
It is impossible to tell that the image is an astrophoto. At this stage, I used to
panic when I first started image processing! I usually select View Range = “Auto”
and Transfer Function = “Auto” in order to inspect the image. A typical CCD
image has 65,000 brightness levels, the overwhelming majority of which the
human eye cannot distinguish. The histogram of the image, a visual graph of the
brightness levels in an image, can be adjusted in order to adjust the information
that is displayed (or hidden) in an image (see Fig. 4.6). Any unacceptable artifacts
(i.e., hot pixels) that remain at this stage are eliminated before any image processing begins. If there is a gradient in the image after flat-fielding, I remove the gradient with an Astroart Gradient Removal plug-in. The software does a respectable
job of correcting the gradient(s). The easiest gradient to fix is one that shows a
change in one direction only. Each Astroart 3.0 plug-in is an external Dynamic
Link Library (DLL) software module. DLL’s are executable functions that can be
used by a windows-based application. The gradient filter corrects vignetting and
sky background gradients, and it is possible to create a synthetic flat field from
the image.
Next, I apply a minimum DDP (Digital Development Process) filter using
Astroart’s default settings. DDP filtering sharpens images and stretches faint portions of an image. I use the default settings for initial filter runs on an image, but
the parameters of the filter can be changed to experiment with the results. The
screen display is again changed (which does not alter the data, only the way they
are displayed) in order to scrutinize the results. Histogram shaping and stretching the image are additional tools that change brightness and contrast values in
an image. At this point, the art of image processing rears its head. No two
imagers will process the same data in the same way. Finding images on the
Internet or in reference books will also show that there is no “standard” to which
to compare one’s image. This is more apparent when doing trichrome imaging.
For monochrome processing (or luminance processing), we are only interested in
image detail, not color. Filters for sharpening and smoothing can be applied next.
An excellent signal in an image is a requirement when using a sharpening filter.
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CCD Astrophotography: High Quality Imaging from the Suburbs
Figure 4.6. Astroart 3.0 screen capture. This FITS image of the Rosette Nebula has been
aligned, coregistered, and stacked and is ready for postprocessing. The histogram above
shows the pixel distribution based on intensity and number of pixels. (Used with permission,
MSB Software, Inc.)
Sharpening tends to highlight or enhance noise if the signal in your image is fair
or marginal. Deconvolution is a special sharpening filter that uses the pointspread function (PSF) of a chosen star. Images are sharpened by removing any
blurring effects that are present. Noisy images are not good candidates for this
filter. The dark halo effect shows up when you are too aggressive with either the
PSF that is chosen or the number of iterations that the filter is used on the image.
In Astroart 3.0, Lucy-Richardson and Maximum Entropy are two deconvolution
(sharpening) filters that, when properly applied, can enhance an image. I usually
apply minimum sharpening features in Astroart 3.0 and then save the image as
both a FITS file and export a bitmap (BMP) copy to yet another program, Corel
Photo Paint (Corel, Inc.). Many imagers continue postprocessing in a graphics
package rather than in one of the astronomy software programs. The final image
should have a sky background that is a very dark gray (not black). I use the
gamma control in Corel to control this, usually starting with a value of 0.9.
Additionally, a powerful image processing tool, Levels and Curves, is also found
in Corel, and when properly mastered, it can be used to mine more data from
your image. I also crop the image to a desired field and resample the image down
from its native almost 12 in. × 16 in (30 cm × 41 cm). The reason for resampling is
that I want the image to fit on a computer screen when I eventually upload the
Processing Astrophotos Made Simple
77
image to my website; it is cumbersome and less pleasing on the eye to have to
scroll around the field to take everything in.
Color composite imaging (trichrome imaging) is another entirely different
ballgame. Color images can be gorgeous, aesthetically pleasing, totally
scientifically inaccurate, and open to a wide variety of interpretations when you
decide on final image presentation. The HX916 camera, like most imaging CCD
cameras, is a monochrome camera. Colored images are obtained by placing
colored filters in front of the camera, one at a time, and later combined with
special software. If you have a full set of hair and are just starting out in
astroimaging and processing, get set for some hair pulling. I cut my teeth on
Astroart 2.0 and have since moved up to Astroart 3.0 exclusively when I process
my images. I learned how to do luminance layering (also known as LRGB processing), which aims to produce a high-quality color image by processing
separate monochrome, red-, green-, and blue-filtered images. The eye judges
sharpness and contrast in the luminance layer, so the goal is to take as long an
exposure as possible and/or combine multiple exposures to make the luminance
image as smooth and pleasing as possible. All histogram changes should be done
on the luminance image so as not to disturb color balance in the filtered images.
Some successful imagers do RGB (red, green, blue) color imaging, depending on
the target being imaged. Some targets, such as globular star clusters and open star
fields, do well imaged with a green filter in place to both record the luminance
frames and the green images. Stars are tight and the luminance image is as pleasing as if a separate clear, IR blocking filter was in place. Still other imagers use
the stacked RGB frames as the luminance channel image during LRGB color
compositing.
One of the benefits of LRGB processing is that if a high-quality luminance
image is taken, unbinned 1×1, and processed as well as possible, the RGB-filtered
images at the telescope can be taken unbinned 2×2, saving time during each integration. Additionally, the quality of the RGB frames does not have to be spot-on
because the higher-quality luminance image layered on top will mask the RGB
frames to some extent. I think of this LRGB technique as allowing the luminance
channel to represent the detail of the image, letting the RGB frames “bleed
through” to reveal their color contribution.
Personally, I take all of my frames unbinned 1×1 and take the time to get as
high-quality frames as I can regardless of whether my clear, red, green, or blue
filter is in the optical train. I think processing is easier and more forgiving when
the quality of the images is better to start with. I do not care much about reducing
the time at the telescope because I do not mind returning to a target on a subsequent night to complete my filtered images. Additionally, the length of each
subexposure is the same regardless of which filter is in place.
A few words about “returning” to a target on a subsequent night of imaging.
First, think about how fortunate we are that the extended objects that we image
are so unimaginably far away and so unimaginably large. Eons can pass and these
objects never change, never alter their appearance. On a subsequent night of
imaging, I open a raw image on my desktop in the observatory, from the previous
imaging session, and then slew the telescope (using TheSky) to get in the general
vicinity of the intended target. I take a few test images and use the cursor in
Astroart 3.0 to mouse-over a few obvious stars that are present in both images. I
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CCD Astrophotography: High Quality Imaging from the Suburbs
take note of the X,Y pixel coordinates of the previous night’s image and use the
Guide speed control on the LX200 paddle to iteratively move the telescope and
camera until a downloaded test image has the star’s pixel coordinates matching
the coordinates on the raw image from the previous night.
The first step in creating a composite image is to approach the luminance and
filtered images as separate routines done in parallel. At the end of the overall
routine, the master LRGB frames are layered on each other to produce a color
image. The luminance processing was covered previously when I discussed
monochrome imaging, so let us start with the RGB frames. Exactly like the luminance image, a master red frame is obtained by first aligning and registering the
calibrated frames (remember that the filtered images have their own dark frames,
flat-field frames, and flat-field dark frames; I use the same bias frames used with
the luminance images) and then Sigma combine the images in Gralak’s program.
This is repeated for the green and blue images.
In Astroart 3.0, the LRGB master images need to be aligned and coregistered
with each other. This means, for example, that a star in the luminance frame at
pixel position (X = 32, Y = 465) needs to be at the exact same position (x-y coordinate) in the red, green, and blue frames. Otherwise, compositing the individual
master frames will not produce pinpoint stars. Astroart has a two-star
align/coregister function that is pretty good at giving consistent results.
A few words on color balancing. Lazy imagers assume that their RGB imaging
filters are close to a 1:1:1 ratio. Astronomik Type II filters are close to this ratio,
but your system (filters and imaging equipment) will yield unique color balancing
factors that will be used during processing. Sun-like (G2V) star data are utilized
to achieve true color balance and apply atmospheric extinction coefficients to
each filtered image. It sounds messy, but it is straightforward. Previously, a G2Vtype star was imaged through each of red, green, and blue filters. AIP4WIN has a
G2V photometry algorithm that allows you to find the correct coefficient multipliers to use with your CCD camera/telescope combination in order to process
the sun like star. In Astroart 3.0, G2V ratios obtained from AIP4WIN are applied
as divisors. For my Astronomik Type II IR-blocked filters, when I image with my
Stellarvue refractor and a Schuler -VIR filter (Schuler, Inc.), my ratios are Red =
0.731, Green = 1.00, and Blue = 0.508. With the LX200 at f/6.3, my ratios are Red
= 0.750, Green = 1.00, Blue = 0.485. The goal is to get the correct color balance (a
white star) so that all of your images, regardless of the target, will have a correct
color balance. No guesswork should be involved. Never having heard about G2V
color balancing, I used to play with the brightness and contrast settings in
Astroart when I first started out in this hobby. It was a nightmare to achieve any
semblance of correct color balance. See Al Kelly’s important paper on this
subject, referenced in Chapter VIII.
Correcting for atmospheric extinction refers to using mathematical factors to
lessen the impact that the atmosphere has on true color balance. The lower the
target that is being imaged is to the horizon (the further the image is away from
the zenith), the more impact that the factor has on achieving correct color
balance.
Now that each master image is color balanced (color multiplier applied to the
master image, extinction coefficient divisor applied to the master image), sky
background color needs to be neutralized. Skyglow is different when viewed
Processing Astrophotos Made Simple
79
through each color filter. Because I have light pollution to contend with, it is
usually greener. When I take separate RGB exposures, each channel will contain
some amount of background sky that will be different from the other channels. If
you look at the histograms before setting the visualization ranges to the same
values in each RGB master, they all look different. If you were to combine them
without making the adjustments, you will get wildly mismatched colors, with the
color starting furthest from the left dominating, and the color frame that starts
closest to the left being almost invisible. Normalizing the background involves
subtracting a constant value from each channel so that the histograms start to
rise at about the same distance from the left.
I open the red, green, and blue master images and look at the “background”
levels in each image’s histogram. I use the “arithmetic,” “add offset” function to
subtract from each frame a value that will leave the background at 500 ADU. For
example, if the background is 1500, I subtract 1000. Next, I increase the white
point slider, using linear scaling, until the object begins to show fairly well in the
green filtered image. Now I look at the visualization minimum and maximum on
the green frame’s histogram and set the same visualization numbers on the red
and blue images, using the “view range” and “user defined” function. If you do
not set each frame to the same white and blackpoint visualization numbers, the
color balance will be affected.
Figure 4.7. Astroart 3.0 screen capture. An aligned and stacked image of the planet
Saturn is shown in its separate red, green, and blue channels. (Used with permission, MSB
Software, Inc.)
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CCD Astrophotography: High Quality Imaging from the Suburbs
Select the “color” button on the Astroart 3.0 menu and select “trichromy.” Use
the defaults and select “okay.” The resulting image is a synthesized RGB image.
The background color should be gray. Adjust the bottom sliders on the color
balance menu until the background meets your satisfaction. The image will look
dim but should not affect the LRGB. To make the LRGB composite, again select
the “color” tab on the Astroart menu and select LRGB synthesis (see Fig. 4.7).
Select your luminance image and select “okay,” and your LRGB image will be
created. The colors might look dull or washed out. If so, select “Color” and then
“Saturation” on the drop-down menu. Increase the saturation to your liking. Are
you done at this point? Are you ever done? Probably not. Further touch-ups,
such as tweaking the color balance, gamma adjustments, and so forth, can be
done in your favorite graphics software program. I save the LRGB image as both a
FITS file and as a bitmap image so that I can further process the image in Corel
(see Fig. 4.8). When I have finished processing the final product (for the time
being!), I save the image as a least-loss JPEG image so that the image remains
small and of high quality for uploading to my website for display.
Figure 4.8. Astroart 3.0 screen capture. An aligned and stacked image of the planet
Saturn is shown, with the color balance selection and high-pass filter windows open. (Used
with permission, MSB Software, Inc.)
CHAPTER FIVE
A Collection of
Astrophotos
All images were taken by the author. Celestial North is up and East is to the left in
each image. After initial processing, each FITS image was saved as a BMP file and
additional processing was done in Corel Photo Paint-8 (version 8.369). Images
were resampled and printed on a Hewlett Packard hp Photosmart 1115 Inkjet
printer, using the following settings: print quality: Best; photo paper: HP
Premium Plus Photo Paper, Glossy; Automatic Image Enhancement (Photo-Ret),
which selects the best combination of print speed and quality. Each image was
saved as a high-resolution BMP image and provided on CD-R to the Publisher.
The following Image Gallery is organized into the following categories: Solar
System, Nebulae, Globular Star Clusters, Galaxies, and Open Star Clusters.
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A. Solar System
Figure 5.1. Cyrillus and Theophilus, LX200 @ f/50. Cyrillus is 62 miles (104 km) in diameter;
Theophilus is 67 miles (100 km) in diameter and has a few prominent mountain peaks rising
from the crater floor.
Figure 5.2. Lunar terminator passing near Clavius, LX200 @ f/10.
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Figure 5.3. Gibbous Moon, Stellarvue Nighthawk @ f/3.6.
Figure 5.4. Plato, LX200 @ f/50. This crater is used to test the resolution of one’s optics. Lunar
orbiter images reveal more than 100 craterlets on the floor of Plato.
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Figure 5.5. Crater Clavius, LX200 @ f/50.
Figure 5.6. Craters, LX200 @ f/10. Panning over the surface of the Moon at any phase is never
disappointing.
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Figure 5.7. Lunar terminator, passing through Clavius, LX200 @ f/20.
Figure 5.8. Alps and Caucasus mountains, LX200 @ f/10. Caucasus mountains rise to a
height of 7.5 miles (12.5 km).
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Figure 5.9. Hesiodus and Hesiodus Rima, LX200 @ f/20, diameter 28 miles (47 km).
There is an obvious gap in the crater wall.
Figure 5.10. Full Moon, Stellarvue Nighthawk @ f/4. Our nearest neighbor, 225,000 miles
away (375750 km). A 3-day trip by rocket.
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Figure 5.11. Mare Nectaris, southwest limb. LX200 @ f/10.
Figure 5.12. Rimae Hippalus and Campanus, LX200 @ f/20. Hippalus is a rile 145 miles
(247 km) long and is a straight valley with deep walls, probably formed as an open
channel in a lava flow.
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Figure 5.13. Copernicus, LX200 @ f/50, diameter 56 miles (93 km). Three central
mountain peaks are evident.
Figure 5.14. Lilius, LX200 @ f/20, diameter 32 miles (93 km). Central mountain peak is
prominent.
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Figure 5.15. Craters, LX200 @ f/10.
Figure 5.16. Clavius, LX200 @ f/20. Sir Arthur C. Clarke’s black monolith of 2001:
A Space Odyssey fame was dug up here.
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Figure 5.17. Plato and Vallis Alpes, a rectilinear fault 700 m wide. LX200 @ f/10.
Figure 5.18. Mare Crisium, LX200 @ f/10, diameter 350 miles (585 km). Site of a large
mason, a gravitational anomaly due to the asteroid impact that created the mare basin.
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Figure 5.19. Apennine and Caucasus mountains, LX200 @ f/10. The Apennine range
stretches 360 miles (600 km) along Mare Imbrium.
Figure 5.20. Jupiter,
LX200 @ f/20. Colorful
wind-driven cloud
bands are seen as
blue, tan, and brown,
with lighter colored
areas called zones.
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Figure 5.21. Jupiter, Io and, Ganymede, LX200 @ f/30. Jupiter is 400 million miles
(650 million km) from Earth. Io and Ganymede are 2 of 28 moons of Jupiter; Io has
extensive volcanism.
Figure 5.22. Jupiter and Great Red Spot, with Io off limb, LX200 @ f/20.
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Figure 5.23. Jupiter and Great Red Spot, with Io off limb and Ganymede’s shadow
transiting, LX200 @ f/20.
Figure 5.24. Jupiter and Great Red Spot, with Io off limb and Ganymede’s shadow
transiting, LX200 @ f/20.
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Figure 5.25. Jupiter and Great Red Spot, with Io off limb and Ganymede’s shadow
transiting, LX200 @ f/20.
Figure 5.26. Jupiter and Io. Great Red Spot transiting near western limb, LX200 @ f/20.
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a
Figure 5.27. (a + b) Jupiter and satellites montage. Left-to-right on each row, 17 images
capture the transit of Ganymede, Io, and, finally, Europa as they move east to west (left to
right) in image sequence, taken 3/21/2004 from 1233 UT to 0341 UT. Images taken with
ToUcam Pro Philips ToUcam Pro PCVC740K webcam (Koninklijke Philips Electronics N.V.)
and LX200 at f/30. Registered and stacked in Cor Berrevoets’ RegiStax version 2.1.13
Beta.
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b
Figure 5.27. Continued
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Figure 5.28. Jupiter, Io and Great Red Spot. Note blue-green festoons, LX200 @ f/20.
Figure 5.29. Jupiter with blue/green festoons, LX200 @ f/20.
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Figure 5.30. Saturn, LX200 @ f/20. Eight hundred million miles (1.3 billion km) from
Earth; it takes 30 years to orbit the Sun.
Figure 5.31. Saturn, LX200 @ f/20.
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Figure 5.32. Saturn,
LX200 @ f/30.
Figure 5.33. Sunspot Complex 484, LX200 @ f/20. This complex appeared in October
2003. It is approximately 87,000 miles (137,000 km) in diameter. Sunspots are
concentrations of magnetic flux and are dark due to their cooler temperatures compared to
the surrounding photosphere.
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Figure 5.34. Sunspot Complex 484, LX200 @ f/20. Meade Series 4000 #12 Yellow
filter used. This complex appeared in October 2003. It is approximately 87,000 miles
(137,000 km) in diameter. Sunspots are concentrations of magnetic flux, and are dark due
to their cooler temperatures compared to the surrounding photosphere.
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Figure 5.35. Mars montage. Top left: image taken August 18, 2003; top right: image
taken August 26, 2003; bottom left: image taken August 30, 2003; bottom right: image
taken August 31, 2003. The closest approach of Mars occurred on August 27 (09:51:14 UT)
at a distance of 55.758 million km, or 34,646,418 miles. At this distance, Mars appeared
larger than at any previous time, 25.11 arc-seconds in diameter, and this was the planet’s
closest approach in 59,619 years. Images taken with ToUcam Pro PCVC740K webcam
(Koninklijke Philips Electronics N.V.) and LX200 at f/50. Registered and stacked in Cor
Berrevoets’ RegiStax (version 2.1.13 Beta.)
Figure 5.36. Mars,
LX200 @ f/30. Note
polar Cap at bottom of
image.
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Figure 5.37. Comet C/2004 F4 Bradfield, Stellarvue Nighthawk @ f/6. A nice tail is
seen extending from the nucleus towards the upper right.
Figure 5.38. Comet C/2004 Q2, Stellarvue Nighthawk @ f/6; also known as comet
Machholz, discovered in 2004. A nice jet is seen to the left, extending from the bright
nucleus.
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Figure 5.39. Comet C/2001 Q4, Stellarvue Nighthawk @ f/6; also known as comet
NEAT, discovered in 2001 by the NEAT Survey. Camera tracked the comet nucleus during
integration, so stars appear red, green and blue when composited.
Figure 5.40. Comet C/2001 Q4, Stellarvue Nighthawk @ f/6; also known as comet
NEAT, discovered in 2001 by the NEAT Survey. Image on right is a negative, used to
enhance any detail in the comet’s tail.
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Figure 5.41. Asteroid
71 Niobe, Stellarvue
Nighthawk @ f/6.
Moving against the
backdrop of the stars,
this 56-mile-diameter
(83-km) rock appears
as a small streak in the
center of this image.
B. Nebulae
Figure 5.42. Horsehead Nebula (B33/IC 434) and Flame Nebula (NGC 2024), Ha
image. Takahashi FS 60-C @ f/6. One of the prettiest and more famous compositions that
all astroimagers strive to obtain each season.
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Figure 5.43. Horsehead Nebula (B33/IC 434) and Flame Nebula (NGC 2024),
Takahashi FS 60-C @ f/6. One of the prettiest and more famous compositions that all
astroimagers strive to obtain each season.
Figure 5.44. Rosette Nebula (NGC 2237), Takahashi FS 60-C @ f/6. Inside the nebula
lies an open cluster of bright young stars that formed about 4 million years ago. The nebular
material and their stellar winds are clearing a hole in the nebula’s center, insulated by a
layer of dust and hot gas.
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Figure 5.45. Flaming Star Nebula (IC 405), Takahashi FS 60-C @ f/6. Ha image. The
nebula is being illuminated by the high-energy star AE Aurigae (embedded in the nebula,
center of image) and is actually moving through the nebula at this time.
Figure 5.46. Cone Nebula and Christmas Tree Cluster (NGC 2264), Takahashi FS 60-C
@ f/6. Ha image. Many stellar nurseries are found within this massive region. Clouds of
gas and dust are buffeted by energetic winds from newborn stars.
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Figure 5.47. Horsehead Nebula (B33), LX200 @ f/6.3, Ha image. Shaped like a chess
knight, this dark cloud of gas and dust shows up in extended integrations but not in an
eyepiece.
Figure 5.48. Emission Nebula IC410, Takahashi FS 60-C @ f/6. Ha image. Diffuse
wreath-shaped emission nebula in Auriga. It resembles a small Rosette. It lies about 2°
southwest of IC 405 (Flaming Star Nebula).
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Figure 5.49. Emission Nebula IC410, Takahashi FS 60-C @ f/6. Diffuse wreath-shaped
emission nebula in Auriga. It resembles a small Rosette. It lies about 2° southwest of IC 405
(Flaming Star Nebula).
Figure 5.50. Cone Nebula and Christmas Tree Cluster (NGC 2264), Takahashi FS 60-C
@ f/6. Many stellar nurseries are found within this massive region. Clouds of gas and dust
are buffeted by energetic winds from newborn stars.
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Figure 5.51. Ring Nebula (M57), LX200 @ f/6.3. The famous ring nebula is often
regarded as the prototype of a planetary nebulae, and recent research has confirmed that it
is actually a ring (torus) of bright light-emitting material surrounding its central star.
Figure 5.52. Dumbbell Nebula (M27), Stellarvue Nighthawk @ f/4.9. This was the first
planetary nebula discovered by Charles Messier.
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Figure 5.53. Dumbbell Nebula (M27), Stellarvue Nighthawk @ f/4.9. Ha image. This
was the first planetary nebula discovered by Charles Messier.
Figure 5.54. Pickerings Triangular Wisp (Veil Complex NGC 6960), Stellarvue
Nighthawk @ f/6. Ha image. The Bridal Veil nebula is a large, complex nebula that spans
over 3o and is the expelled remnants of a supernova.
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Figure 5.55. Cocoon Nebula (IC 5146), Stellarvue Nighthawk @ f/6. Ha image. This
nebula is located about 4000 light-years away toward the constellation of Cygnus. Inside
the Cocoon is a newly developing open cluster of stars. Like other stellar nurseries, the
Cocoon Nebula is an emission nebula, a reflection nebula, and an absorption nebula.
Recent measurements suggest that the massive star in the center of the image opened a hole
in an existing molecular cloud and now provides the energy source for much of the emitted
and reflected light from this nebula.
Figure 5.56. Cocoon Nebula (IC 5146), Stellarvue Nighthawk @ f/6. Ha image.
Resampled 150%. This nebula is located about 4000 light-years away toward the
constellation of Cygnus. Inside the Cocoon is a newly developing open cluster of stars. Like
other stellar nurseries, the Cocoon Nebula is an emission nebula, a reflection nebula, and
an absorption nebula. Recent measurements suggest that the massive star in the center of
the image opened a hole in an existing molecular cloud and now provides the energy
source for much of the emitted and reflected light from this nebula.
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Figure 5.57. North American Nebula (NGC 7000) and Pelican Nebula (IC5067-70)
composite image, Stellarvue Nighthawk @ f/4.9. Ha image. Only a portion of NGC 7000
is shown. On a dark night under a clear and transparent sky, the North American Nebula
can be seen with the unaided eye as a bright patch in the Cygnus Milky Way. The Pelican
Nebula lies about 2000 light-years away in the constellation of Cygnus, the Swan. The two
glowing nebulae appear separated from our vantage point by a large obscuring dust cloud.
Figure 5.58. Horsehead Nebula (B33), Stellarvue Nighthawk @ f/4.9. Ha image.
Shaped like a chess knight, this dark cloud of gas and dust shows up in extended
integrations but not in an eyepiece.
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Figure 5.59. Open Star Cluster NGC 6910, Sadr, and surrounding nebulae, Stellarvue
Nighthawk @ f/6. Ha image. The third brightest star of Cygnus, called Gamma Cygni or
Sadr (the bright star right of center of the photograph), is surrounded by a huge complex of
emission nebulosity. The nebula, which extends well beyond the borders of this image, is
excited by young, hot blue-white stars and separated by dark nebulae into at least five
major parts.
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Figure 5.60. Great Nebula in Orion (M42). Stellarvue Nighthawk @ f/6.0. Ha composite
image. Immense cloud of gas is 1500 light-years away. It can be seen with the naked eye
at dark sites. The trapezium is at the center of the nebula and requires shorter integrations
due to the brighter stars located here.
Figure 5.61. Network Nebula (NGC6992). Stellarvue Nighthawk @ f/6. Ha image.
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Figure 5.62. Pac Man Nebula (NGC 281), Stellarvue Nighthawk @ f/4.9. Ha image.
Busy area of intense star formation. Dark Bok globules, black blobs visible against the
brighter nebulosity, are areas of intense star formation.
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Figure 5.63. Lace-Work Nebula and Cirrus Nebula NW Part. Stellarvue Nighthawk
@ f/6. Ha image. The Bridal Veil nebula is a large, complex nebula that spans over 3° and
is the expelled remnants of a supernova.
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Figure 5.64. Bubble Nebula (NGC 7635), Stellarvue Nighthawk @ f/6. Ha image. As
fast moving gas expands from a nearby star, it pushes the surrounding gas into a shell. The
energetic starlight then ionizes the shell, causing it to glow.
Figure 5.65. Nebula Complex IC 1396 and surroundings, Stellarvue Nighthawk
@ f/4.9. Ha image. One of the largest emission nebulae in the universe, it spans 3°. The
Elephant Trunk can be seen in the lower right of this image.
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Figure 5.66. Open Star Cluster M52 and Bubble Nebula (NGC 7635), Stellarvue
Nighthawk @ f/6. As fast-moving gas expands from a nearby star, it pushes the
surrounding gas into a shell. The energetic starlight then ionizes the shell, causing it to glow.
Figure 5.67. Bubble Nebula (NGC 7635), Stellarvue Nighthawk @ f/6, cropped. As
fast-moving gas expands from a nearby star, it pushes the surrounding gas into a shell. The
energetic starlight then ionizes the shell, causing it to glow.
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Figure 5.68. Emission Nebula NGC 1893, Stellarvue Nighthawk @ f/6. Ha image.
Figure 5.69. Emission Nebula IC1795, Stellarvue Nighthawk @ f/6. Ha image. Very dim
emission nebula with dark dust lanes.
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Figure 5.70. Flame Nebula (NGC 2024), Stellarvue Nighthawk @ f/6. Ha image. Bright
star Alnitak, easternmost star in Orion’s Belt, lights up the Flame Nebula.
Figure 5.71. California Nebula (NGC1499). Portion taken with Stellarvue Nighthawk
@ f/6. Ha image.
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Figure 5.72. Heart of Rosette Nebula (NGC 2237), Stellarvue Nighthawk @ f/6. Ha
image. Inside the nebula lies an open cluster of bright young stars that formed about
4 million years ago. The nebular material and their stellar winds are clearing a hole in the
nebula’s center, insulated by a layer of dust and hot gas.
Figure 5.73. Open Star Cluster M52 and Bubble Nebula (NGC 7635), Stellarvue
Nighthawk @ f/6. Ha image. As fast-moving gas expands from a nearby star, it pushes the
surrounding gas into a shell. The energetic starlight then ionizes the shell, causing it to glow.
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Figure 5.74. California Nebula (NGC 1499), Takahashi FS 60-C @ f/6. Ha image. The
California Nebula gets its name from its resemblance to the United States’ most populous
state and is located 1000 light-years from our solar system. It is believed to be illuminated
by the star Xi Persei, the fourth-magnitude star at the top of the image. Although large in
size, this nebula has a low surface brightness, which makes it difficult to detect visually.
Figure 5.75. Crescent Nebula (NGC 6888), Stellarvue Nighthawk @ f/6. Ha image. This
nebula is about 25 light-years across and was created by winds from the bright star seen
near the center of the nebula. NGC 6888’s central star should ultimately go out with a
bang, creating a supernova explosion in 100,000 years.
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Figure 5.76. Horsehead Nebula (B33), LX200 @ f/6.3.
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Figure 5.77. Emission Nebula IC443, Takahashi FS 60-C @ f/6. Ha image. Supernova
remnant, looks to many like a jellyfish. A neutron star is buried deep within this nebula.
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Figure 5.78. Flaming Star Nebula (IC 405), Takahashi FS 60-C @ f/6. The nebula is
being illuminated by the high-energy star AE Aurigae (embedded in the nebula, center of
image) and is actually moving through the nebula at this time.
Figure 5.79. Crab Nebula (M1), LX200 @ f/6.3. Ha image. Supernova remnant of a star
that exploded in AD 1054. A pulsar is at the center of the envelope of tendrils.
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Figure 5.80. Dumbbell Nebula (M27), LX200 @ f/6.3. Ha image. This was the first
planetary nebula discovered by Charles Messier.
Figure 5.81. Dumbbell Nebula (M27), Stellarvue Nighthawk @ f/4.9. Ha image. This
was the first planetary nebula discovered by Charles Messier.
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Figure 5.82. Great Orion Nebula (M42) and Running Man Nebula (NGC 1977), Stellarvue
Nighthawk @ f/6. NGC 1977 is a reflection nebula and appears blue because the blue light
from the neighboring stars scatters more efficiently from nebula gas than does red light.
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Figure 5.83. Great Nebula in Orion (M42). Takahashi FS 60-C @ f/6. Immense cloud of
gas 1500 light-years away. It can be seen with the naked eye at dark sites. The trapezium
is at the center of the nebula and requires shorter integrations due to the brighter stars
located here.
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Figure 5.84. Ring Nebula (M57), Stellarvue Nighthawk @ f/6. The famous ring nebula is
often regarded as the prototype of a planetary nebulae, and recent research has confirmed
that it is actually a ring (torus) of bright light-emitting material surrounding its central star. A
wide-field image places the nebula in context against the vastness of space.
C. Globular Star Clusters
Figure 5.85. Globular Star Cluster M71, LX200 @ f/3.3. A very loose globular star
cluster that is a part of a small and unique group of globulars with metal-rich stars.
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Figure 5.86. Globular Star Cluster M5, Stellarvue Nighthawk @ f/6. M5, located in the
constellation of Serpens Caput, is one of the three great globulars, ranking with M13 and
M3.
Figure 5.87. Globular Star Cluster M3. Stellarvue Nighthawk @ f/6. Like all globulars,
this huge ball of stars predates our Sun. Long before our Earth existed, ancient globs of stars
condensed and orbited a young Milky Way Galaxy. Of the 250 or so globular clusters that
survive today, M3 is one of the largest and brightest.
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Figure 5.88. Hercules Globular Star Cluster M13, LX200 @ f/6.3. One of the brightest
and largest globulars visible to northern hemisphere observers.
Figure 5.89. Hercules Globular Star Cluster M13, Stellarvue Nighthawk @ f/4. One of
the brightest and largest globulars visible to northern hemisphere observers.
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Figure 5.90. Hercules Globular Star Cluster M13, Stellarvue Nighthawk @ f/6. Cropped.
Figure 5.91. Globular Star Cluster M22, LX200 @ f.6.3.
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Figure 5.92. Globular Star Cluster M3, LX200 @ f/6.3. Like all globulars, this huge ball
of stars predates our Sun. Long before our Earth existed, ancient globs of stars condensed
and orbited a young Milky Way Galaxy. Of the 250 or so globular clusters that survive
today, M3 is one of the largest and brightest.
D. Galaxies
Figure 5.93. Spiral Galaxy M33, Stellarvue Nighthawk @ f/6. The Triangulum galaxy
M33 is a prominent member of the Local Group of galaxies. Several knots in the spiral arms
of M33 have been assigned their own NGC catalog numbers.
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Figure 5.94. Spiral Galaxy M106, Stellarvue Nighthawk @ f/6. This galaxy is
distinguished by arms, or jets, seen curving outward through the disk in optical emission lines.
Recent measurements near the nucleus suggest a supermassive dark object (a black hole
candidate with mass on the order of 100 million solar masses) at the center of this galaxy.
Figure 5.95. The Great Andromeda Galaxy M31, Stellarvue Nighthawk @ f/6. This is a
portion of the Andromeda Galaxy, the nearest major galaxy to our own Milky Way
Galaxy. Our Galaxy is thought to look much like Andromeda. Together these two galaxies
dominate the Local Group of galaxies. The diffuse light from Andromeda is caused by the
hundreds of billions of stars that comprise it.
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Figure 5.96. Spiral Galaxy NGC 2543, Stellarvue Nighthawk @ f/6, cropped.
Figure 5.97. Spiral Galaxy NGC 2903, Stellarvue Nighthawk @ f/6. This barred spiral
galaxy is estimated to be 20 million light-years away. This is one of the objects Messier
missed for some reason—its magnitude of 9.6 is in the brightness range of other Messier
galaxies. NGC-2903 is also known as a “starburst galaxy” and has been the subject of
Hubble Space Telescope studies.
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Figure 5.98. Spiral Galaxy UGC 3587, Stellarvue Nighthawk @ f/6.
Figure 5.99. Galaxies UGC 4042, UGC 4039, CGCG 148-33, and UGC 4032,
Stellarvue Nighthawk @ f/6.
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Figure 5.100. Galaxies NGC 3185, NGC 3189, NGC 3187, and MCG4-24-22,
Stellarvue Nighthawk @ f/6. The central three galaxies are part of the Hickson 44 Group in
the constellation Leo.
Figure 5.101. Barred spiral galaxy NGC 3432, Stellarvue Nighthawk @ f/6. NGC
3432 is interacting with a faint nearby galaxy PGC 32617 located between the tic marks.
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Figure 5.102. Spiral Galaxies NGC 2968 and NGC 2964, Stellarvue Nighthawk @ f/6.
Figure 5.103. Spiral Galaxy NGC 2862, Stellarvue Nighthawk @ f/6.
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Figure 5.104. Blackeye Galaxy (M64), Stellarvue Nighthawk @ f/6. Known for its dark
arc-shaped dust region.
Figure 5.105. Sombrero Galaxy (M104), Stellarvue Nighthawk @ f/6. Well-known dust
lane. Disk and bulge have a mass of several billion Suns.
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Figure 5.106. Spiral
Galaxy M74 (NGC
628), Stellarvue
Nighthawk @ f/6. This
spiral galaxy is an
island universe of about
100 billion stars,
30 million light-years
away toward the
constellation Pisces.
M74 presents a
gorgeous face-on view
and is similar in many
respects to our own
Milky Way Galaxy.
Figure 5.107. Edge-on Spiral Galaxy NGC 891, Stellarvue Nighthawk @ f/6. The
galaxy’s disk is so thin that the spiral galaxy appears edge-on. The dark band across the
middle is a lane of dust that absorbs light.
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Figure 5.108. Edgeon Spiral Galaxy
NGC 891, cropped.
Stellarvue Nighthawk
@ f/6. The galaxy’s
disk is so thin that the
spiral galaxy appears
edge-on. The dark
band across the middle
is a lane of dust that
absorbs light. Cropped.
Figure 5.109. Edgeon (Needle) Galaxy
IC2233, Bear Paw
Galaxy (NGC 2537)
and Spiral Galaxy
NGC 2537A,
Stellarvue Nighthawk
@ f/6.
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Figure 5.110. Leo Triplet Galaxies M65, M66, and NGC 3628, Stellarvue Nighthawk
@ f/6. All are part of the same group of galaxies at a distance of 65 million light-years from
Earth.
Figure 5.111.
Whirlpool Galaxy
(M51), LX200 @ f/6.3.
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Figure 5.112. Whirlpool Galaxy (M51), Stellarvue Nighthawk @ f/6.
Figure 5.113. Spiral
Galaxy NGC 2543,
Stellarvue Nighthawk
@ f/6.
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Figure 5.114. Sculptor Galaxy (NGC 253), Stellarvue Nighthawk @ f/6. Largest member
of Sculptor Group of Local Galaxies, nearest group to our own Milky Way Group.
E. Open Star Clusters
Figure 5.115. Open Star Cluster NGC 6705, Stellarvue Nighthawk @ f/6. Also known
as the Wild Duck Cluster, it is one of the richest and most compact known open clusters,
with an estimated 2900 stars.
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Figure 5.116. Open Star Clusters NGC 869 and NGC 884, Stellarvue Nighthawk
@ f/6. Also known as the Double Cluster in Perseus, this unusual cluster is bright enough to
be seen from a dark location without binoculars.
Figure 5.117. Open Star Cluster M103, Stellarvue Nighthawk @ f/6. Bright blue stars
highlight the open cluster known as M103. The gas clouds from which these stars
condensed has long dispersed. Of the stars that were formed, the brightest, bluest, and most
massive have already used up their nuclear fuel and self-destructed in supernova explosions.
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Figure 5.118. Open Star Cluster NGC 1528, Stellarvue Nighthawk @ f/6. Open star
cluster in Perseus.
Figure 5.119. Open Star Cluster NGC 663, Stellarvue Nighthawk @ f/6. Open star
cluster in Cassiopeia.
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Figure 5.120. Open Star Cluster NGC 743, Stellarvue Nighthawk @ f/6. Only 15 stars
to this group, with the center clear of stars.
Figure 5.121. Open Star Cluster NGC 1582. Stellarvue Nighthawk @ f/6.
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Figure 5.122. Open Star Cluster NGC 6819, Stellarvue Nighthawk @ f/6. Also known
as The Foxhead star cluster in Cygnus.
Figure 5.123. Open Star Cluster M34, Stellarvue Nighthawk @ f/6. This intermediateaged open cluster of about 100 stars lies about 1400 light-years distant and is scattered
over 35 arc-minutes, more than the diameter of the Full Moon.
A Collection of Astrophotos
Figure 5.124. Open Star Clusters M35 and NGC 2158, Stellarvue Nighthawk @ f/6.
Open star cluster M35 consists of several hundred stars and is scattered over the area
covered by the Full Moon (30 arc-minutes).
Figure 5.125. Open Star Cluster M36 (NGC 1960), Stellarvue Nighthawk @ f/6.
Considered one of the youngest open star clusters at 20 million years of age.
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Figure 5.126. Open Star Cluster M37, Takahashi FS 60-C @ f/6. M37 is the brightest of
the three open clusters in southern Auriga.
Figure 5.127. Open Star Clusters M38 and NGC 1907, Takahashi FS 60-C @ f/6.
M38’s brightest stars form a pattern resembling the Greek letter pi.
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Figure 5.128. Open Star Cluster M39, Stellarvue Nighthawk @ f/6. M39 is a very large
and very loose open cluster, only 800 light-years distant. Thirty stars are proven members.
Figure 5.129. Open Star Cluster M44, Stellarvue Nighthawk @ f/6. Also called Praesepe
(Latin for “manger”), or the Beehive cluster. It is one of the open star clusters easily visible to
the naked eye and thus known since prehistoric times.
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Figure 5.130. Open Star Cluster M46 with Planetary Nebula NGC 2438, Stellarvue
Nighthawk @ f/6. The cluster is very rich, with 150 stars. A famous feature is planetary
nebula NGC 2438, appearing within the apparent borders of M46. This object appears to
lie near the northern fringes of the cluster, but is a passing guest.
Figure 5.131. Open Star Clusters M47 and NGC 2423, Stellarvue Nighthawk @ f/6.
Open cluster M47 is a bright cluster that can be glimpsed with the naked eye under good
conditions as a dim nebulosity. It is a coarse cluster of approximately 50 bright stars.
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Figure 5.132. Open Star Cluster M50, Takahashi FS 60-C @ f/6. Open cluster M50 is
probably about 3200 light-years distant and has an estimated population of about 200
stars in the main body.
Figure 5.133. Open Star Cluster M67, Takahashi FS 60-C @ f/6. M67 is one of the
oldest known open star clusters at 3.2 billion years which is much less than the age of our
Solar System.
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Figure 5.134. Open Star Clusters NGC 869 and NGC 884, Stellarvue Nighthawk
@ f/6. Also known as the Double Cluster in Perseus, this unusual cluster is bright enough to
be seen from a dark location without binoculars. Luminance imaged through green filter.
Figure 5.135. Open Star Cluster/Nebulosity NGC 1931, Stellarvue Nighthawk @ f/6.
NGC 1931 is a tiny little cluster of stars embedded in nebulosity . At the heart of the cluster
lies a tiny version of the famous Trapezium in M42; four stars that make a rough trapezoid.
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155
Figure 5.136. Open Star Cluster NGC 457, Stellarvue Nighthawk @ f/6. This open star
cluster, also known as the ET Cluster, lies in the constellation Cassiopeia. It contains more
than 100 stars and lies at a distance over 9000 light-years away.
Figure 5.137. Open Star Cluster NGC 7209. Stellarvue Nighthawk @ f/6.
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Figure 5.138. Open Star Cluster NGC 663, Stellarvue Nighthawk @ f/6. Open star
cluster in Cassiopeia. Luminance imaged through green filter.
CHAPTER SIX
What to Do with
All Those
Astrophotos
Many of us who take astrophotos want to share them with anyone who is interested. My children are 11 years old. I must admit that after 3 years of trying to
achieve higher-quality images and trying to improve my image processing skills,
I think they are warming to the idea that astrophotos can be interesting to look at.
My wife is supportive, but she is quick to ask me “haven’t you imaged this
before?” when I show her a new image. “Once an open star cluster always an open
star cluster” is her mantra. Well, you get the picture. Unless you share the passion
for this hobby of ours, I guess the 100th open star cluster or wide-field galaxy
imaged at 2.84-arc-seconds/pixel resolution begins to look the same. For me, a
wide-angle image that captures a galaxy that is only 2 arc-minutes in longest
dimension against the backdrop of enormous blackness and sprinkled stars—
there is majesty in this image. I like the context that such an image conveys. I
have tried to explain to my kids that the fuzzy blob they were staring at in an
image was so unimaginably big and yet so far away despite its apparent size on
the image. They could not comprehend that a few hundred billion stars were contained in that ovoid smudge in the image. How many people can?
There are several storage media to choose from so that your hard drive does
not fill to capacity too quickly. Each night’s imaging session gets recorded to a
CD-R disk (capacity 750 MB). When I do tricolor imaging, an evening’s session
can easily fill several disks. Additionally, many imagers save several iterations
during the processing routine. After trying a particular filter or processing step,
the intermediate image is saved so it can easily be revisited.
Some imagers save their final images in JPEG or BMP format and burn them to
a CD-R so the images can be hand-delivered to a photo processing place. You
might be dismayed at the overall color of your images when you get them printed
by a 1-h photo store or lab. Sky backgrounds in the images can be wild, spanning
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the colors of the rainbow. Why don’t the prints look like the pictures in the magazines and on the Web? There are a variety of reasons that the sky background
can be different colors. A likely one is that the sky really does have some color
from man-made light pollution, but the overriding cause is that the automatic
printing machine and operator at the photo lab just do not know what to do with
an astronomy picture. Our images can contain lots of blackness or be almost
completely blank except for some dots (stars). Try to work with the actual person
who does the printing at the 1-h lab. See how much control the operator has and
if they are interested in helping you.
When your images are digitized, you can adjust them yourself and then print
them on your inkjet printer or laser printer. I bought a Hewlett Packard high-end
inkjet printer and have had some success printing lunar and planetary images.
One of the proprietary software programs that came bundled with the printer
allows a lot of image manipulation in a real-time window, which looks very
similar to the printed image. However, open star clusters and nebulae with wispy
elements do not print well on my inkjet printer.
Computer monitor calibration is extremely important, not only for viewing
true fidelity of your color and monochrome images but also to preview your
image for eventual printing. There are devices and bundled software that can
accomplish this, as well as Internet websites that have special gray scales and
color bars that the user can reference as his or her monitor is adjusted.
Unfortunately, not all imagers keep their monitors calibrated, and if you like to
post your images to a website or view the images of others, you need to keep this
in mind when scrutinizing images.
If you decide to print your own images, the printer is the ultimate decisionmaker when it comes to the quality of your printed photos. Your Printer’s Device
Options will allow you to change your printer’s ability to produce great printed
photos. The important settings to look for are: print quality settings and paper
type. You should set the print quality to the highest setting and select the correct
paper type. If you select the “Plain Paper” setting but print on premium photo
paper, the results will be less than optimal. Consumer Reports, here in the United
States, reviewed photo paper for inkjet printers (Consumer Reports, January,
2005) and came to the following conclusions: Generic photo glossy paper [100
sheets for $15.00 (8.10£)] is not worth the time or expense. The results were
extremely poor. Professional Grade photo paper is recommended and the added
expense is worth the results.
I was introduced to online photo printing by a fellow astroimager. I have used
iphotoshop.com for almost 2 years and have had the good fortune of only having
the postal service ruin my printed images once. The company now uses sturdy
photo mailing tubes to return photos regardless of the size of your order. This
service allows you to digitally upload your highest-quality formatted image using
three different methods: an FTP (File Transfer Protocol) server, a traditional
website, or uploading after installing a company freeware utility called a print
wizard. With FTP uploading, you organize your images into a folder on your local
computer and either drag the folder to a window on the company’s website or
directly FTP transfer. This service uploads faster than standard Web upload and
uses the optimum file resolution for the selected print size. Web uploads allow all
of your photos (regardless of print size desired) to be uploaded using a file
What to Do with All Those Astrophotos
159
upload interface. (Depending on your browser version, you can either “drag and
drop” your files all at once or browse for them individually). When the upload is
complete, you will see a thumbnail preview of each image. You can now select the
print size and quantity for each image. Finally, the Print Wizard is a free application that gets installed onto your system to help you process online digital print
orders quickly and easily. Uploads are faster than standard Web upload and FTP,
which is great for users with slower connections and/or users uploading a large
order.
A handful of quality lunar images taken at f/30 with the LX200 and ToUcam
camera looked so good on my monitor that I uploaded them to iphotoshop.com
and had several poster-size images printed with a matte finish. Behind nonglare
glass, matted and framed, this collection of lunar landscapes usually draw comments from guests to my house, incredulous that they were not beamed back
from one of the lunar orbiters! I have also used the online photo service for
resampling some of my open star clusters and colorful nebulae shots to a reasonable 16-in. × 20-in. (41-cm × 51-cm) or 24-in. × 30-in. (61-cm × 76-cm) image.
There is some cost savings realized by getting photo mounting spray glue and
mounting and framing the images yourself.
Designing a website can be as simple as uploading JPEG photos to an imagehosting site or spending lots of money for a fully functional Web portal where
you control everything. There are also choices in between the extremes. I am
computer-savvy but do not know anything about Web Page construction and
design. I chose PBase galleries to host my JPEG images because for a nominal fee
of around $20 (10.80£) annual, I have unlimited storage and ease of use. The great
thing about having your own website is the instantaneous ability to share images
by clicking and pointing. I designed a site that organizes my images into folders
(galaxies, nebulae, solar system, and so forth) and have thumbnails for quick
reference.
Sky & Telescope and Astronomy are two magazines that many of us subscribe
to that encourage readers to send in our best images for consideration in their
Gallery section. If one of your images does not make it into the Gallery section,
many photos taken by amateurs also make it into the body of an article, or if a
special feature that is discussed needs a photo of the Moon or Jupiter, for
example, one of our prize images is substituted for a stock photo. It is nice to recognize familiar names in print of imagers with whom we might correspond on
any of the Internet groups.
CHAPTER SEVEN
An Introduction
to Minor Body
Astrometry
On February 17, 2005 OakRidge Observatory was given an official observatory
designation (H76). An observatory code is assigned by the Minor Planet Center
(MPC) upon receipt of acceptable observations of minor bodies (asteroids and
comets). This is a pretty exciting honor. The MPC is responsible for the designation of minor bodies in the solar system: minor planets, comets, and natural
satellites. The MPC is also responsible for the efficient collection, computation,
checking, and dissemination of astrometric observations and orbits for minor
planets and comets. Several publications, such as the Minor Planet Circulars, are
issued throughout the year in print and electronic format.
Astrometry is the precise measurement of the position and motion of astronomical objects, with respect to standard star catalogs. Newcomers to astrometric
observing are required to observe a number of low-numbered, known minor
planets each on pairs of nearby nights. If weather interferes, the two observing
nights can be nonconsecutive. After reporting two or three observations of each
object from each night, a specially formatted MPC Report is submitted and the
positions are checked against known astrometric solutions. The quality of the
observations, measured in arc-seconds, is reported back to the observer. An
observatory code is assigned upon acceptance of an initial submitted batch of
observations.
It is expected that an observer can produce good astrometry of known objects
before beginning to discover new objects. It is important that observers can consistently produce observations with an accuracy of less than 1 arc-second for
observations using the same comparison stars, and the night-to-night consistency should be limited only by the comparison star catalog. (One arc-second
refers to a measurement within a 1-arc-second circle of the predicted asteroid
position.)
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Through April 2005 I have logged 40 total observations (residuals) on 6 known
minor bodies, with 36 astrometric solutions having an accuracy less than 2 arcseconds (90%). My R.A. error is +0.05 ± 0.99 and my Dec. error is +0.10 ± 0.83.
Not bad for having one of the smallest, if not the smallest, aperture telescopes
(78 mm) being used of all the reporting observatories in the world. There are 1160
listed observatory codes, updated nightly, though April 13, 2005.
One problem with looking for minor planets under a light-polluted sky is the
ability to discern these small rocks at much beyond magnitude 17 or 18. My
approach thus far to recording known minor planets on CCD images is to use
TheSky to search for extended minor planets at a specific area of the sky, near my
local zenith, where it is darker. I frame an area with the FOV indicator, orient the
view in the virtual sky to match my camera, and look for suitable targets. I can
slew with the LX200, take a few test images, and match apparent asterisms (or
patterns; you typically cannot see the minor body even with a dramatic screen
stretch). With the STV guider tracking through the LX200, I can snap an image of
180–300 s integration every 15 min for up to 1 h or so; during the 15-min inter-
Figure 7.1. Astroart 3.0 screen capture. Astrometry is the precise measurement of the
position and motion of astronomical objects, with respect to standard star catalogs such as
the Guide Star Catalog (GSC) that Astroart uses. A portion of the Rosette Nebula
(NGC 2246) is shown on the left, with four small circles marking the position of four known
stars, as shown in the Star Atlas at right. The window at bottom shows the R.A. and Dec
coordinates, as well as the stellar magnitude, of these four stars. (Used with permission, MSB
Software, Inc.)
An Introduction to Minor Body Astrometry
163
lude the minor planet moves against the backdrop of the “fixed” stars, and when I
subsequently align the images on the stars, there should be one minor planet (or
more) moving between image frames.
Astroart 3.0 has a “blink” function that allows each image to be compared to
the other at various speeds in order to best spot the moving body against the
fixed background. I can also use AIP4WIN to make an AVI loop, replaying the
small movie of several frames. If I spot the known minor planet where it should
be (TheSky shows minor planet positions for any time and any time interval), I
can easily mark the FITS image with a centroid marker. Astroart 3.0 has both an
astrometric and photometric tool, but the software and creation of an MPC
Report is unstable with my Windows operating system (see Fig. 7.1).
Instead, I use Software Bisque’s CCDSoft and TheSky to perform an astrometric solution on my images, whether I can see the minor planet or not.
(Sometimes, even with a dramatic screen stretch, the minor planet that is supposed to be there, right next to an obvious star, is just not there. Chalk it up to
light pollution.) An inventory of every star from your CCD image is created (see
Fig. 7.2). Using the approximate equatorial coordinates from the FITS image’s
header (which is copied from the Astroart 3.0 FITS header because the camera
Figure 7.2. CCDSoft version 5 screen capture. Raw image of galaxy NGC3432 has been
opened and astrometric solution completed. Twenty-five stars were used in the solution,
marked with yellow crosses in original. RMS, RMS X and RMS Y values are all very good.
Image scale is 2.87 arc-seconds/pixel. White streak at center is galaxy NGC3432,
stretched. (Used with permission, Software Bisque, Inc.)
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that I use is a non-SBIG camera: otherwise, it is automatically supplied by TheSky
when the image was taken if using an SBIG camera), Image Link pattern recognition then determines the stars from your image that match stars from the Guide
Star Catalog and/or the stars from the Hipparcos/Tycho stellar catalog.
Accurate star centroids are computed for each star, and a six-coefficient linear
plate solution (astrometric solution) is computed using all available stars (see
Figs. 7.3 and 7.4). The Astrometry dialog box is presented, showing the precise
right ascension and declination of the center of the image, the image scale in arcseconds/pixel, the image’s position angle, the overall root mean square (RMS)
value, as well as astrometric data for each individual star used in the solution.
Computed residual error, measured in arc-seconds, is the amount by which the
star’s position varies from the catalog position.
Amateur astronomers often contribute to activities such as helping to track
asteroids and observing occultations to determine both the shape of asteroids
and the shape of the terrain on the edge of the Moon. In the past, amateur
astronomers have also played a major role in discovering new comets. Recently,
Figure 7.3. TheSky version 5, Level 4 screen capture. CCDSoft has completed a successful
astrometric solution and has successfully linked the image with TheSky. The rectangle frames
the FOV of the telescope and CCD camera and shows galaxy NGC3432 at center.
Asteroid 76694, a magnitude 18.55 extended minor planet moving at 0.0012 arcseconds/s, is seen at left of FOV. During a 300-s integration, the asteroid will have moved
approximately 0.12 pixels. Circle with arrowed vector denotes direction and movement
over ensuing 24 h. (Used with permission, Software Bisque, Inc.)
An Introduction to Minor Body Astrometry
165
Figure 7.4. CCDSoft version 5 screen capture. Raw image of galaxy NGC3432 has been
opened and astrometric solution completed. “Insert Minor Planets” command has been
selected and a circle (green in original) has marked the location of the only known minor
planet in the FOV at the time of image capture. The FITS header has been opened to show
the detected body is minor planet 76694. Streak at right of FITS information box is galaxy
NGC3432. (Used with permission, Software Bisque, Inc.)
however, funding of projects such as the Lincoln Near-Earth Asteroid Research
and Near Earth Asteroid Tracking projects has meant that most comets and asteroids are now discovered by automated systems, long before it is possible for amateurs to see them.
Just locating an asteroid is an achievement! Well, software certainly makes
things easier, but the observer can still prepare for a night of imaging asteroids.
Armed with an ephemeris (table of predicted positions), a star chart, and software, the problem is greatly reduced. Plotting the position on the star chart will
enable you to recognize the brighter asteroids immediately or else to narrow the
search down to a few possible stars. Final recognition depends on determining
which “star” is moving. Over the period of an hour, most asteroids will reveal
their identity against the background. Having found a moving body on your CCD
images, what do you do? Well, you can prepare an MPC Report and wait for
confirmation of a minor body having been captured by your CCD camera or you
can first use software, such as Find Orb, to first test the quality of your astrometric observations. Let us say that you record the position of a moving body several
times and feed the results to Find Orb. If you see that their positions line up
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nicely on an orbit with residuals of around 1 arc-second, you will start to feel
much better about the quality of your astrometry.
Even relatively simple observations can be instructive. Photometry, the measurement of apparent magnitudes of astronomical objects, can also be conducted.
Does the apparent brightness of a moving body change during the course of an
evening as the asteroid spins on its axis? Some elongated asteroids have large
amplitudes. By estimating the brightness at regular intervals over two or three
nights it is possible to derive an axial rotation period very accurately. Even if the
brightness does not appear to change during the course of a night, it will change
as the distance from the Earth changes, brightening as opposition approaches
and fading as the Earth draws ahead after opposition.
Although amateur observers still contribute many valuable Near Earth Orbit
(NEO) observations, their most significant contributions have evolved away
from NEO discovery toward astrometric follow-up (observations to help refine
the orbits of new NEOs discovered by the professional surveys) and valuable
physical studies to help better characterize the physical nature of these planetary
projectiles.
Recording known asteroids on CCD detectors is fun but not necessarily challenging. A small investment in time is all that is necessary, as you typically need
to record three or four images, spaced 15–20 min apart, on two separate nights. I
usually plan a deep sky imaging session with this time commitment in mind. That
is for known asteroids. The real fun is the prospect that on any (and maybe all) of
your deep sky images lurks a moving body that might be an undiscovered asteroid! During a 3-h imaging session, I might align and coregister three images (first,
middle sequence, and end) in Astroart 3.0 and manually blink the images. Three
images might represent Time0, Time +90 min, and Time +180 min. You can play with
the screen stretch to best visualize the background of your images. What appears
to be a moving object might very well be a group of hot pixels, dust mote artifact,
or maybe an asteroid! To better visualize the movement of the object over the
entire 3 h of imaging, I align and coregister the images in AIP4WIN after darkframe subtracting and flat-fielding and then load the calibrated images into an
AVI file. You can watch a time-compressed loop over and over, looking for the
moving object against the background. If the motion is obviously impossible (i.e.,
the object has retrograde motion or flies out of the frame at an acute angle), you
have just wasted an hour: You have not recorded an asteroid. You can also do an
astrometric solution on a few frames in CCDSoft and TheSky, generate an MPC
Report, and run a few observations through the Find Orb software.
No other branch of science allows the naming of new worlds by the discoverer.
The discoverer of a new asteroid has the privilege of suggesting a name to the
15-member Committee for Small-Body Nomenclature of the International
Astronomical Union, which judges its suitability. This committee is composed of
professional astronomers (with research interests connected with minor planets
and/or comets) from around the world. The assignment of a particular name to a
particular minor planet is the end of a long process that can take many years.
This would be a nice way for someone to leave their mark on astronomy.
CHAPTER EIGHT
Invaluable
Contacts and
Links
There are so many dedicated imagers out there who have helped me immensely
over the last 3 years. I have saved much of the “important” email correspondence
over the years (the Pearls of Wisdom) in a binder with tabbed dividers, which has
made the job of organizing this book easier. Special thanks must go out to Jon
Talbot, Alan Chen, Al Kelly, Paul LeFevre, Paul Kane, Terry Platt, Daniel Bisque,
Rod Mollise, Al Testani, Bob Holzer, Michael Downing, Fabio Cavicchio, R.A.
Greiner (Doc G.), Ron Wodaski, Charlie Warren, and the late Bruce Johnston.
These guys patiently (I hope) answered many of my questions; many continue to
do so. I am sure I have forgotten several others. If my imaging results fall short of
the reader’s expectations, the fault is all mine! Please do a GOOGLE search on any
of these imagers and see what quality astroimaging is all about.
“Acquiring and Processing
Astronomical CCD Images”
Adirondack Video Astronomy
Amateur Astronomy Feature at the
National Air and Space Museum
Astroart User Group
AIP4WIN User Group
Anacortes Telescope and Wild Bird
Art and Science of CCD Astronomy
Astroart 3.0 User Group
Astromart
http://www.ghg.net/akelly/procccd.htm
http://www.astrovid.com
http://www.nasm.si.edu/exhibitions/
gal111/universe/firstlight/observers.cfm
http://groups.yahoo.com/group/AstroArt
http://groups.yahoo.com/group/AIP4WIN
http://www.buytelescopes.com/default.asp
Ratledge, David (Ed). Springer, 1996
http://groups.yahoo.com/group/
AA3Plugins
http://www.astromart.com/default.asp?
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CCD Astrophotography: High Quality Imaging from the Suburbs
Astronomik
Astronomy magazine
“At Home in a Dome”
Atomic Clock Sync
Backyard Astronomer’s Guide
Belkin Corporation
Choosing and Using a
Schmidt–Cassegrain Telescope
Clear Sky clock online
Consolidated Lunar Atlas
Corel Photo Paint
“Drift Method of Polar Alignment”
Ephemeris Generator
Ephemeris Time Spans
Find Orb
FRcalc.exe software
Gateway computers
“G2V Color CCD Balancing”
The Handbook of Astronomical
Image Processing (AIP4WIN)
Heavens-Above
High Resolution CCD Imaging
Interactive NGC Catalog
International Dark Sky Association
iphotoshop
Jerry Lodriguss Image Index
Jim’s Mobile, Inc.
K3CCD Software
Kendrick Astro Instruments
Le Sueur Manufacturing Company
Light Pollution in Europe
Losmandy Astronomical Products
Lumicon
“LX200 Polar Alignment”
LX200 User Group
MAPUG
MEADE Instruments
Meade Uncensored User Group
Messier Catalog
http://www.astronomik.com/english/
eng_contact.html
http://www.astronomy.com
http://www.homedome.com/online.htm
http://www.worldtimeserver.com/
atomic-clock
Dickinson, Terrance and Alan Dyer.
Firefly Books, LTD, 2002
http://world.belkin.com
Mollise, Rod. Springer, 2001
http://cleardarksky.com
http://www.lpi.usra.edu/resources/cla/
http://www.corel.com
http://www.aa6g.org/Astronomy/
articles.html
http://ssd.jpl.nasa.gov/cgi-bin/eph
http://ssd.jpl.nasa.gov/eph_spans.html
http://www.projectpluto.com/find_orb.htm
http://www.aquest-inc.com/
downloads.htm
http://gateway.com
http://www.ghg.net/akelly/artdraf7.htm
http://www.willbell.com/AIP/Index.htm
http://www.heavens-above.com
http://legault.club.fr/index.html
http://www.seds.org/~spider/ngc/ngc.html
http://www.darksky.org
http://www.iphotoshop.com
http://www.astropix.com/HTML/K_MISC/
TOC_DEX.HTM
http://www.jimsmobile.com/index.htm
http://www.pk3.org/Astro
http://www.kendrickastro.com/astro/
index.html
http://www.astropier.com
www.inquinamentoluminoso.it/dmsp
http://www.losmandy.com
http://www.lumicon.com
http://www.astrocruise.com/polarnew.htm
http://groups.yahoo.com/group/LX200
http://www.mapug.com/index.htm
http://www.meade.com
http://groups.yahoo.com/group/
Meade-Uncensored
http://seds.lpl.arizona.edu/messier/xtra/
history/m-cat.html
Invaluable Contacts and Links
Minor Planet Center
Moon and Sun Rise/Set tables
online
Moon-“light” Atlas online
MSB Astroart 3.0 software
Mueller’s Atomics
The New CCD Astronomy
National Optical Astronomy
Observatory Image Gallery
National Service Radar
The NGC/IC Project
Night Sky magazine
Observatories User Group
Oceanside Photo and Telescope
Orion Telescopes and Binoculars
Parks Optical
PBase.com
Philips
QCUIAG User Group
RealVNC Software
Registax software
SBIG Santa Barbara
SBIG STV User Group
ScopeStuff
SCT User Group
Sigma Combine
Sky & Telescope magazine
Sloan Digital Sky Survey
SoftBisq User Group
Software Bisque
Spaceweather.com
Starlight Xpress™
Starlight Xpress™ User Group
Stars
Stellarvue® Telescopes
Stellarvue® User Group
Adam Stuart’s Gallery
Takahashi America
TelescopeService
The STScI Digitized Sky Survey
169
http://cfa-www.harvard.edu/cfa/ps/
mpc.html
http://aa.usno.navy.mil/data/docs/
RS_OneYear.html
http://www.astrosurf.com/cidadao/
moonlight.htm
http://www.msb-astroart.com
http://www.muellersatomics.com
Wodaski, Ron. The New Astronomy
Press, 2002
http://www.noao.edu/image_gallery
http://www.srh.noaa.gov/radar/latest
http://www.ngcic.org
http://nightskymag.com
http://groups.yahoo.com/group/
Observatories
http://www.optcorp.com/default.aspx
http://www.telescope.com
http://www.parksoptical.com
http://www.pbase.com
http://www.pc-cameras.philips.com
http://groups.yahoo.com/group/QCUIAG
http://www.realvnc.com
http://registax.astronomy.net
http://sbig.com
http://groups.yahoo.com/group/SBIGSTV
http://www.scopestuff.com
http://groups.yahoo.com/group/sct-user
http://www.gralak.com/Sigma/index.html
http://skyandtelescope.com
http://www.sdss.org
http://groups.yahoo.com/group/
SoftBisqUser
http://www.bisque.com
http://spaceweather.com
http://www.starlight-xpress.co.uk
http://groups.yahoo.com/group/
starlightxpress
http://www.astro.uiuc.edu/~kaler/sow/
class-g.html
http://www.stellarvue.com
http://groups.yahoo.com/group/Stellarvue
http://www.pbase.com/adamstuart
http://www.takahashiamerica.com
http://www.telescopeservice.com/
services.htm
http://stdatu.stsci.edu/cgi-bin/dss_form
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CCD Astrophotography: High Quality Imaging from the Suburbs
Technical Innovations
“What is Drift Alignment?”
http://www.homedome.com
http://members.aol.com/ccdastro/
drift-align.htm
Glossary
Achromat A type of refractor whose objective is made from lenses of different
materials, selected to bring two colors of light (usually blue and yellow) to the
same focal point. The rest of the colors of visible light are brought almost to the
same focal point, but because they all do not arrive at the same focal point or
plane, there is some color distortion around bright point sources.
ADU Value Analog-to-Digital Units. These are the raw numbers that emerge
from a CCD camera and represent the counts per pixel read out from a CCD.
Aggressiveness Term used when making guiding adjustments. An aggressiveness setting of 1 means that the SBIG STV guider will make the full correction
that it calculates it needs to make; a setting of 0.5 means that it will make half
the calculated move. Setting a number to less than 1 helps reduce oscillation or
overshoot.
Altizmuth/Azimuth Mount Short for Altitude–Azimuth (also called Alt-Az).
Telescopes that are mounted so that they move up-down and left-right (as
opposed to equatorially) are called Alt-Az. This is a typical configuration for
visual use on a traditional tripod.
Aperture The term as used with a telescope refers to the opening at the front of
the tube that allows light through; the diameter of the objective of a telescope.
Apochromat
aberration.
A type of telescope that lacks both spherical and chromatic
Astigmatism An optical defect in which star images are elongated into ovals
that change from a radial orientation (pointing toward the center of the field) to a
tangential one (at right angles to the center) as the telescope focuser is moved
from one side of best focus to the other.
Asterism Pattern of apparently neighbored, but physically unrelated stars,
formed by a chance alignment of the stars at different distances that happen to be
situated in about the same direction. A famous asterism is the Big Dipper.
Astrometry The precise measurement of the position and motion of astronomical objects, such as asteroids and comets, with respect to standard star catalogs.
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Atmospheric Extinction Coefficient Imaging a target other than near the zenith,
its light travels a longer distance through the Earth’s atmosphere before it can
reach you. A coefficient is determined for each colored filter and imaging setup
that is used to color-correct for those photons that are absorbed and scattered by
the atmosphere at nonzenith angles.
Autoguider A CCD that is attached to a guide scope and electronically attached
to the control of the telescope mount. It monitors the position of a guide star on
the CCD chip and adjusts the telescope’s drives to keep the star in the same position. This enables long-exposure astrophotography by correcting for drive errors
and polar alignment errors.
AVI Loop An AVI file video format that can be played on popular computer
software. A loop means that the small file is played continuously, restarting after
the video file ends.
Backlash Term describing the amount of play between gears. Use of zeroimage-shift Crayford focusers, modifying the Meade Superwedge, and P.E.C.
training the LX200 are examples of trying to improve or eliminate backlash.
Barlow Lens Barlow is a negative (diverging) lens that is placed between the
objective lens (or primary mirror) and the eyepiece of a telescope. It increases the
effective focal length of an objective lens, thereby increasing the magnification.
Assuming that the Barlow is a good lens, the only disadvantage is a slight loss of
light that hits your retina or CCD chip.
Bias Frame An image of almost zero exposure time, with no light reaching the
CCD detector.
Binning Binning involves combining pixels on a CCD chip to create larger
pixels. For example, one pixel that is binned becomes a 2×2 square of pixels and
creates one pixel that is twice the width and four times the area of the original
pixel. This is done to increase sensitivity or to match a long-focal-length telescope to a CCD camera with small pixels. Unbinned is also written as 1×1
binning.
Black Point A histogram adjustment that will determine the amount of shadow
detail in an image. It is considered proper to set the black point so that the
darkest part of an image will just have zero detail.
Blue Bloat Refers to an RGB (red, green, blue) image acquired with an achromat
that has blue channel bloating. The stars in the image will appear to have blue
halos because of the blue bloat.
Bortle Scale To help observers judge the true darkness of a site, John Bortle
created a nine-level scale based on nearly 50 years of observing experience. The
scale goes much beyond estimating one’s limiting magnitude.
Glossary
173
CCD Charge-coupled device. A type of image sensor used in some astronomical
cameras. When a picture is taken, the CCD is struck by light coming through the
telescope lens to which the camera is attached. Each of the thousands or millions
of tiny pixels that make up the CCD converts this light into electrons. The
number of electrons are measured and then converted to a digital value, which is
recorded by a computer that is attached to the camera.
Centroid As used in image processing, refers to the X,Y-coordinate of a star’s
center position, usually compared to the expected position as determined from a
reference stellar catalog.
Chromatic Aberration In a refractor, light passes through a lens and is bent to
reach a focus point. Each wavelength of light is bent differently, so they do not all
meet at the same point of focus. The result is an out-of-focus glow, usually
purple or blue in color because the violet light is least likely to meet focus with
the other colors. Some refractors are specially corrected for this aberration. CCD
cameras are far more sensitive to ultraviolet and infrared light than the human
eye, so only the very best refractors are suitable for high-resolution CCD imaging.
My Stellarvue Nighthawk is an achromat.
Collimation The process of aligning the elements of an optical system.
Collimation is routinely needed in SCTs and requires simple adjustments of the
secondary mirror on the Meade LX200 by turning three screws.
Coregister Term used in image processing. Refers to aligning images, regardless
of orientation or telescope-CCD camera configuration used to take the image, so
all stars and extended objects line up pixel for pixel.
Corrector Plate The glass lens on the front of an SCT. Because an SCT uses
spherical mirrors that suffer from spherical aberration, the corrector plate is used
to eliminate this aberration.
Cosmic Ray Hits Charged particles moving at nearly the speed of light that
reach the Earth from space and hit the CCD detector. These events are recorded
on the CCD image as small streaks and need to be processed out.
Crayford Focuser A type of telescope focuser in which the focus tube is moved
by a roller. These focusers are known for smooth, slack-free motion and for precisely adjustable friction.
Dark Current Astronomical CCDs can detect electronic noise generated by the
CCD chip itself. The amount of noise created by the CCD chip is known as dark
current. Dark current is a function of temperature, and cooling the CCD chip can
remove much of the noise. The remaining noise is eliminated with dark frames.
Dark Frame A dark frame is a CCD image taken with the lens cap on the telescope, of the same duration as the light image. This image detects noise gener-
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ated by dark current. Using image processing software to subtract the dark
frame from the raw image leaves only the object. The dark noise is eliminated.
DDP Filter DDP stands for Digital Development Processing. This an image
processing routine used in many software programs. DDP processing allows
both bright and dim parts of an astronomical object to be displayed at the same
time. DDP essentially compresses washed-out regions of an object into a range
that the computer can display.
Declination (Dec.) Declination is one of the coordinates in a system used by
astronomers to locate celestial bodies in the sky. Declination is measured in
degrees and refers to how far above the imaginary “celestial equator” an object is.
It is similar to latitude on the Earth. Declination is measured as 0° at the celestial
equator, +90° at the North Pole, and –90° at the South Pole.
Declination Drift Even if the seeing is excellent, if a telescope’s mount is
not polar aligned with good accuracy, there will be a slow north or south drift
in declination (i.e., the star will slowly drift from its original location). Drift
polar aligning is accomplished by monitoring the declination drift of a star at
high power in the eyepiece and adjusting the polar axis of the mount based on
the direction of drift. See Chuck Vaughn’s treatment of this referenced in
Chapter VIII.
Device Manager A tool that is included with the Microsoft Windows operating
system; it can display and control the hardware that is attached to a computer
running MS Windows. When a piece of hardware (i.e., a CCD camera) is not
working properly, the offending hardware is highlighted in yellow and the user
can attempt to troubleshoot the conflict.
Download time As used with a CCD camera attached to a computer, it is a
measure of the time it takes for images to appear on the computer monitor after
an exposure ends. USB download connections are faster than parallel port, and
binned images download faster than unbinned images.
Ephemeris The coordinates of a planet, sun, comet, or moon given at regular
intervals of time. The standard format can be downloaded to popular planetarium programs (such as Software Bisque’s TheSky) to locate these celestial bodies
in real time or to plan for an upcoming observing or imaging session.
Equatorial Mount An equatorial wedge is used for imaging with a forkmounted telescope. An equatorial wedge mounts between the telescope and pier
to allow the forks to be aimed toward Polaris so that the telescope can track in
just one axis, eliminating field rotation.
Ethernet The most widely installed local area network (LAN) technology. The
most commonly installed Ethernet system is called 10BASE-T and provides transmission speeds up to 10 Mbps, allowing several computers to transfer data over a
communications cable.
Glossary
175
Extended Deep Sky Object Deep sky objects (DSOs) include the enormous
variety of nebulae, star clusters, and galaxies beyond our solar system. DSOs
appear extended: They have a visible size, rather than just being a single pinpoint
of light like an individual star.
Extended Minor Planet Term as used in Software Bisque’s TheSky. It refers to
minor planets that can exceed 30,000 objects in inventory and are computed for a
given instant in time and remain visible on the Virtual Sky for only a specified
period.
Field of View (FOV) The two dimensional area that can be seen through the
telescope and CCD imaging system. It is expressed in arc-minutes or degrees,
depending on how small (or large) the CCD chip is when used with a given
optical system.
Field Rotation If the mount is not polar aligned correctly, field rotation will
result. This refers to stars at the edge of the image frame appearing to rotate
around the guide star.
FITS Standard Stands for Flexible Image Transport System. A file written in this
standard format conforms to the specifications and endorsement of the
IAU (International Astronomical Union) for transfer of astronomical data.
Flat Field Out-of-focus dust particles in the optical system and vignetting can
lead to an unevenly illuminated CCD chip. By taking an image of an evenly illuminated source (such as the evening sky after sunset or the inside of an observatory dome), the differences in illumination across the field of view can be
removed using image processing software.
Focal Ratio (f/ratio) The f/ratio of a telescope is determined by dividing the
focal length of the primary lens or mirror by the aperture (the diameter of that
same lens or mirror). This number tells us several important things about a telescope. The lower the f/ratio the faster the telescope is said to be; that basically
means that it provides a brighter image than a similar sized telescope with a
higher f/ratio. Telescopes with low f/ratios give wide-field images with bright star
fields; they are good for viewing star clusters and faint nebulae. Telescopes with
high f/ratios do not deliver views as bright but yield higher magnifications with
narrower fields of view. They are ideal for planet viewing.
Focal Reducer A focal reducer is used to reduce the focal length of a telescope
objective. It is a converging lens and helps to increase the “speed” of the
telescope.
FWHM Full-width-at-half-maximum. This numeric value reflects the approximate size of a star’s image as seen by the eye. It is shaped like a Gaussian curve
and is the width across the profile when it drops to half of its peak, or maximum,
value. It is a well-defined number that can be used to compare the quality of
images obtained under different observing conditions.
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G2V Star A term that refers to a spectral type of star. The Sun is a G2V star,
meaning that it is a “G” star, subclass 2, and of luminosity class V, signifying
Main Sequence. G2V stars are considered known white-source stars and are used
for calibrating filters used for trichrome imaging.
Galaxy A system of about 100 billion stars. Our Sun is a member of the Milky
Way Galaxy. There are billions of galaxies in the observable universe.
Globular Star Cluster A spherical cluster of thousands and thousands of stars,
formed at the same time billions of years ago. Globular clusters usually have a
size of 50–150 light-years.
GPS Telescope Global Positioning System. A system of relay satellites sends
information to a receiving device on a telescope and computes the position of the
observer on the Earth. It eliminates the need with computer-controlled telescopes
to go through the alignment routine when setting up. This type of telescope is
probably more meaningful to someone who does not have a permanent setup.
Gradient The departure from an even background in an image. It is usually
seen when tangential light enters the telescope optics and is recorded by the CCD
chip as a nonuniform grade.
GSC Catalog The Guide Star Catalog I (GSC I) is an all-sky catalog of positions
and magnitudes of approximately 19 million stars and other objects in the 6th to
15th magnitude range. The GSC 1 catalog is used for the control and target selection of the Hubble Space Telescope. GSC 2.2 contains almost 450 million objects.
Guiding No telescope mount can track perfectly. For CCD imaging, it is necessary to very accurately track the object being imaged. This is done by guiding on
a star and making small mount corrections as the star is followed. This makes up
for any errors in the telescope’s drive system. Guiding can be done manually by
watching a star through a crosshair eyepiece or by using an autoguider such as
the SBIG STV.
Hartmann Mask A full aperture mask with two or three holes cut in it. When
placed over the front of a telescope, it causes multiple images of a star when the
star is out of focus. When in focus, the star’s images converge to become one.
Hipparcos Catalog The Hipparcos star catalog contains 118,218 stars. The
Hipparcos Catalog is one of the primary products of the European Space
Agency’s astrometric mission, Hipparcos, which operated from 1989 to 1993,
returning high-quality data.
Histogram A histogram is a graph of the number of pixels versus pixel values in
an astronomical image. Pixel values run from lowest (displayed as black, to the
left on the graph) to highest (displayed as white, to the right on the graph). A bar
is plotted for each pixel value showing the number of pixels in the image with that
value. An astronomical image typically has more pixels toward the lower end of
the histogram because most astroimages contain large amounts of dark sky.
Glossary
177
Host/Client The Local Network is comprised of the observatory computer
(Host) and control room computer (Client). The Host computer provides Client
users with services such as database access and typically has the software on it on
which the Client computers depend.
Hydrogen-alpha Filter This is a filter that is designed for CCD imaging of
gas and planetary nebulae. Due to the narrow bandpass of the H-alpha line at
656 nm, the filter provides maximal increase in contrast even under poor observing conditions. The 13-nm bandwidth of the Astronomik H-alpha filter allows
transmission as high as 97%.
Image Calibration/Reduction Refers to modifying the raw CCD data after it is
obtained. This is where dark frames, flat fields, and bias frames (and their matching dark frames) are applied.
IR-Blocked Digital sensors are infrared (IR) sensitive. IR-blocking filters are
used to block spurious responses from color filters when doing trichromy.
Light Box An internally illuminated box that uses indirectly placed light sources
to evenly illuminate a translucent diffuser screen (milk plastic or vellum) on one
side of the container. The screen is sized to cover the entire aperture of the telescope so that accurate flat-field frames can be made.
Light-Pollution-Rejection Filter These filters generally work by blocking wavelengths of light that interfere with the object you are trying to view or image.
Light-pollution filters work by blocking the scattered light from mercury vapor
lights and other terrestrial light sources.
Light-Year The distance that light, moving at a constant speed of 186,000 miles
per second (300,000 km per second), travels in 1 year. One light-year is about
6 trillion miles, or 10 trillion km.
Limiting Magnitude The magnitude of the dimmest star that you can see at the
zenith (overhead). It is determined by weather, local light-pollution, and viewing
techniques.
LRGB Images taken with a black-and-white CCD camera through red, green,
and blue filters are combined to make RGB images. We get most of the spatial
information about an image from the brightness, or luminance, portion of the
image, not from the color, or hue, portion. This means that it is possible to take a
lower-resolution color image and combine it with a high-resolution black-andwhite image to make an LRGB image (the L stands for luminance). As long as the
low-resolution color image is combined with a high-resolution luminance image,
the full resolution is maintained and the total exposure time is decreased.
Luminance The monochrome (high-resolution) portion of an image.
Magnitude Scale A system of ranking stars by apparent brightness. The brightest stars in the sky are categorized as being of first magnitude, and the faintest
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stars visible to the naked eye are classified as sixth magnitude. The scheme
extends to cover stars and galaxies too faint to be seen by the unaided eye.
Increasing magnitude means fainter stars, and a difference of five magnitudes
corresponds to a factor of 100 in apparent brightness. The brightest star visible
with the naked eye is over 600 times brighter than the faintest one. The Sun is
over 6 trillion times brighter than the faintest star visible to the naked eye.
Median Combine Noisy images can be smoothed to some extent by taking the
median value of all the pixels in the images when image processing. Median combining requires that there be an odd number of images (e.g., you can median
combine 9 images, but not 10).
Memory Buffer Also called a memory cache, it is a portion of computer
memory made of high-speed Static Random Access Memory (SRAM) instead of
the slower and less expensive dynamic RAM (DRAM) used for main memory.
Memory caching is effective because most programs access the same data or
instructions over and over. By keeping as much of this information as possible in
SRAM, the computer avoids accessing the slower DRAM.
Meridian Transit This is the passage of a celestial body across the observer’s
meridian, coincident with the time when the object reaches its highest point in
the sky. The meridian is an imaginary great circle projected on the sky, passing
through the North and South poles at right angles to the equator.
Messier Objects The original 110 objects are a set of astronomical objects
(galaxies, nebulae, open star clusters, and globular star clusters) cataloged by
Charles Messier in his catalog of nebulae and star clusters, first published in 1774.
The original motivation behind the catalog was that Messier was a comet hunter
and was frustrated by objects that resembled but were not comets.
Micron The length of one-millionth of a meter, or 1/1000000 m (~ 1/25,000 in.)
This length is also referred to as a micrometer.
Mirror-Lock The LX200 Classic design is prone to image shift when focusing. A
primary mirror-lock completely cancels any residual image shift while focusing
during CCD imaging when using a Crayford-style focuser, which moves the eyepiece holder and not the telescope mirror once locked.
Mirror Slop Refers to the focus shift that is caused by the primary mirror when
it slides on the baffle tube (all moving-mirror Cassegrains have some mirror
slop).
Monochrome Refers to having a single color, typically referring to a black-andwhite image.
MPC Report Astrometric observations of comets, minor planets, and natural
satellites are submitted for publication in the Minor Planet Circulars (MPC),
Minor Planet Electronic Circulars and IAU Circulars, and are represented by
Glossary
179
80-column records. The format differs depending on whether the observation is
optical (photographic, CCD, or visual), radar, or satellite based.
Nebula A diffuse mass of interstellar dust and gas.
Network A connection of two or more computers that can share resources.
Noise Unwanted, random variations in brightness or color that is always
present to some extent within any signal. The information captured by a CCD
sensor contains both image data and noise.
Nyquist Sampling Theorem The law that is the basis for sampling continuous
information. It states that the frequency of data sampling should be at least twice
the maximum frequency at which the information might vary. Applied to CCD
imaging, if we want to accurately reproduce a telescope image, the resolution of
the CCD should be twice the resolution of the telescope.
Open Star Cluster A cluster of stars usually containing several hundred
members packed into a region usually less than 20 light-years in size. They are
normally found near regions of star formation in the spiral arms of galaxies.
Opposition The position of a planet when it is exactly opposite the Sun as seen
from Earth. A planet at opposition is at its closest approach to the Earth.
Oversampled If too many pixels are gathered by a CCD camera, no additional
information is afforded, and the image is said to have been oversampled. The
extra pixels do not theoretically contribute to improving the spatial resolution.
Parallel Port A port on the computer that is faster than a serial port but slower
than USB. Often used by printers and flash card readers.
Parfocal A term that refers to both eyepieces and filters. With eyepieces, a
change in magnification maintains an image that remains in focus. With filters,
the claim means that an object being imaged remains in focus despite a change in
filter. My Astronomik Type II filters are advertised as parfocal and they are close,
but the focus still needs adjustment with an achromat refractor and the LX200.
P.E.C. Training Every set of drive gears has some inherent inconsistencies that
will manifest as a time-varying tracking rate. In the case of the LX200’s right
ascension (R.A.) gears these errors repeat every 8 min. The Smart Drive function
of Meade’s LX200 telescope allows one to train the computer to compensate for
periodic errors in the drive’s R.A. gears. This is more commonly known as periodic error correction, or PEC. Training the Smart Drive of your LX200, similar to
doing an accurate polar alignment, is one of the best ways to improve the quality
of your photographs.
Photometry Photometry is the measurement of apparent magnitudes of astronomical objects, like stars or asteroids.
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Photon Visible light behaves like a wave phenomenon, but in other respects it
acts like a stream of high-speed, submicroscopic particles arranged in discrete
packets. These high-energy packets travel through empty space at a speed of
approximately 186,000 miles (300,000 km) per second.
Pixel Pixel is short for picture element and describes the tiny squares that make
up a CCD image. Pixels can also refer to the individual squares in an image or the
actual light-sensitive squares on a CCD chip (also called photosites).
Planetary Nebula As a star collapses, the outer gaseous layers are ejected into
space and resemble a planet like ball of gas.
Plate Solution Another term for object’s solution, which is the precise measurement of an astronomical objects position and motion.
Polar Alignment “Equatorial” telescope mountings have two axes (a polar axis
and a declination axis) to help compensate for the Earth’s rotation and aim at
objects in different parts of the sky. The polar axis of an equatorial mount
should point at the north celestial pole and the process of accomplishing this is
called “polar aligning.” This means making the polar axis of the mount parallel
to the Earth’s axis of rotation. This greatly simplifies the tracking of a celestial
object across the sky, requiring only the motion of the telescope’s mount in
right ascension. For long-exposure deep sky astrophotography, polar alignment
is critical.
Quantum Efficiency (QE) As photons of light hit a CCD chip, they are converted
into electrons that are stored and then read out at the end of the exposure. Not
every photon that hits the chip is converted into an electron. How many photons
are converted depends on the camera’s QE. QE is expressed as a percentage of
the number of photons converted. If all the photons produced electrons, the QE
would be 100%. Most amateur CCD cameras have QEs in the range 25–50. Film
has a typical QE of around 2%.
Raw Frame
produces.
The downloaded, unprocessed FITS image that the CCD camera
Refractor This is what most people think of as a traditional telescope: It has a
lens at one end and you look straight through the other. This is sometimes
referred to as a “Galilean” telescope, as it is of the same design that Galileo used.
Residuals Used in astrometry, this term describes the observed position of a
celestial body compared to the predicted position. A residual of 0 would imply
precise location. Low residuals are an indication of quality data.
Resolution The ability of a telescope to measure the angular separation of
objects in an image that are close together. Also, it refers to the level of detail that
a CCD camera can capture, usually expressed in arc-seconds per pixel. Smaller
pixels produce a higher resolution, meaning that smaller details can be seen.
Glossary
181
Reticle A system of lines and/or concentric circles incorporated into an eyepiece, used for positioning or guiding the telescope, or polar-aligning an equatorial mount. The Meade 9mm reticle is illuminated in order to render the lines
visible against a dark background sky.
Right Ascension (R.A.) Right ascension is one of the coordinates in a system
used by astronomers to locate celestial bodies in the sky. It is similar to longitude
on the Earth. Right ascension is measured in hours of time, from 0 to 24.
RMS Value This is a complicated mathematical term—the square root of the
average of the squares (root mean square) of the instantaneous values. It is the
square root of the arithmetical mean of the squares. For our purposes, it refers to
overall RMS (root mean square) error of an astrometric solution. Values under
0.50 indicate a very good solution.
Schmidt-Cassegrain (SCT) A classic wide-field telescope. The first optical
element is a Schmidt corrector plate. The plate is produced by placing a vacuum
on one side and grinding the exact correction required to correct the spherical
aberration caused by the primary mirror. It is placed in front of the mirror and
intercepts the light as it enters the telescope. The Schmidt corrector is thicker in
the middle and the edge. This corrects the light paths so that light reflected from
the outer part of the mirror focuses at the same point as light reflected from the
inner portion of the mirror.
Sidereal Rate Time measured relative to the fixed stars. The sidereal day is the
period during which the Earth completes one rotation on its axis. Because the
Earth moves in its orbit about the Sun, the sidereal day is about 4 min shorter
than the solar day and a given star will appear to rise 4 min earlier each night, so
that different stars are visible at different times of the year.
Sigma Combine Sigma is a type of mathematical averaging used in image processing routines with automatic rejection of bright and dark pixels, much more
powerful than the simple median combine, with a better SNR ratio.
Signal-to-Noise Ratio (SNR) For our purposes, it is the ratio between the magnitude of a light signal (meaningful information) and the magnitude of background noise. SNR is the true test of a CCD camera’s detection capability. All
scientific CCD camera manufacturers attempt to maximize the signal (the
number of available full-well electrons) and minimize the noise (electrical and
thermal) in order improve the camera’s performance.
Slew This term refers to moving the LX200 telescope with the hand paddle or
using the artificial crosshair cursor in TheSky to point and select a target. You can
then command the telescope to slew, or move, to the intended target.
Software Driver A program that interacts with a particular device or special (frequently optional) kind of software. The driver contains special knowledge of the
device or special software interface that programs using the driver do not have.
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Star Bloat This term refers to the appearance of brighter stars in an image
during extended integrations. You can tame star bloat by shortening integration
times and possibly perform some image processing to further reduce the bloat.
Star Diagonal A telescope accessory that contains a mirror or prism that
redirects a beam of light upward for more convenient viewing. A star diagonal
typically fits into a focuser, has an eyepiece fitted into it, and bends the light path
through a right angle. Some imagers use a CCD camera in place of the eyepiece in
order to control camera orientation.
Summing Images Because astronomical objects tend to be faint, it is often
desirable to add CCD images together to increase the detail visible in the image.
This process is known as summing. Summing images will also increase the noise
in the image, but not at the same rate that signal builds.
Two-Line Element (TLE) Orbital data for any satellite tracking program, such as
contained in Software Bisque’s TheSky, are referred as two-line elements. They
are updated regularly by CelesTrak and can be downloaded in specially formatted
files from the Internet directly into a software program.
Tracking Mount The stars appear to move because of the motion of the Earth. If
you are using a telescope for astro imaging, you will need to have a telescope with
a clock drive that “follows” them. The quartz clock moves the mount and telescope at a sidereal rate.
Trichrome Color Imaging Most astronomical CCD cameras are inherently
black-and-white. To take color images, red, green, and blue filters are placed in
the imaging train in order to isolate each color. Each image is then subsequently
combined using image processing software to create a color image.
Two-Star Alignment Built-in procedure in the LX200 computer that allows
the user to align the telescope with the sky by first selecting two stars, approximately 50–90° apart. This initializes the telescope when in altizmuth/azimuth
configuration.
Tycho Catalog Another stellar catalog, Tycho is complete to magnitude 10.5 and
contains almost 3 million stars.
Undersampled If too few pixels are utilized when imaging, then all of the spatial
details comprising the image will not be present in the final image.
USB A serial connection technology that is almost universally available in
current computers. Version 1.x allowed for 12-Mbps transfer rates, and this was
boosted to 480-Mbps for USB 2.0.
Vignetting Vignetting is a darkening of the corners of an image, usually caused
by light falling off toward the edge of the CCD chip due to the optical system. It is
typically seen with an SCT and a focal reducer and is often removed by using a
flat field.
Glossary
183
Virtual Sky Software Bisque’s TheSky graphically represents the night sky and
telescope position with a virtual sky. It is the main window that shows the stars,
planets, galaxies, and other celestial objects.
White Point A histogram adjustment that will determine the amount of highlight detail in an image. It is considered proper to set the white point so that the
lightest part of an image will just have zero detail.
Zenith The point that is directly above the observer on the imaginary sphere
against which celestial bodies appear to be projected.
Formulas
1.
f/ratio of optical system
f/ratio = FL/aperture
where FL = focal length.
2.
Focal length of system
FL = (pixel size × 206)/resolution
where pixel size is in microns and resolution is in arc-seconds/pixel.
3.
Limiting visual magnitude
m = 6.5–5 log Delta+5 log D = 2.7+5 log D
(assuming transparent dark sky conditions), where m is the approximate
limiting visual magnitude, Delta is the pupillary diameter (in mm) (accepted
value 7.5), and D is the diameter of the objective (in mm).
4.
Dawes limit (smallest resolvable angle)
Theta = 115.8/D
where Theta is the smallest resolvable angle (in seconds) and D is the diameter of the objective (in mm). Atmospheric conditions seldom permit Theta <
0.5 arc-seconds.
5.
Resolution of lunar features
Resolution = [2 × (Dawes limit × 3476)/1800]
Dawes Limit = 115.8/D
where Resolution is the smallest resolvable lunar feature (in km), D is the
diameter of the objective (in mm), 2 × Dawes limit is the Airy disk (a more
practical working value is twice this); 1800 is the angular size of the moon (in
seconds), and 3476 is the diameter of the Moon (in km).
6.
Magnification of optical system
m = FL OTA/FLep
where m is magnification, FL is focal length, OTA is the optical tube assembly
of the telescope, and ep is eyepiece.
185
186
7.
CCD Astrophotography: High Quality Imaging from the Suburbs
Maximum allowable tracking error
S ~ 8250/(F × E)
where S is the error (“slop”) (in arc-seconds), F is the focal length (in mm),
and E is the amount of enlargement of the image.
8.
Apparent angular size of an object
Theta = (h/D) × k
where Theta is the object’s apparent angular size (in units corresponding to
k), h is the linear height of the object (in units corresponding to D), D is the
distance of the object (in units corresponding to h), Theta is the object’s
angular height (angle of view) (in units corresponding to k), k is a constant
with a value of 57.3 for Theta (in degrees), 3438 (in minutes of arc), or
206,265 in [seconds of arc (the number of the respective units in a radian)].
9.
Range of useful magnification of a telescope
Minimum useful magnification
Best visual acuity
Wide views
Lowest power to see all detail (resolution
of eye matches resolution of telescope)
Planets, Messier objects, general viewing
Normal high-power, double stars
Maximum useful magnification
Close doubles
Limit imposed by atmospheric turbulence
0.13×D
0.25×D
0.4×D
0.5×D
0.8×D
1.2×D to 1.6×D
2.0×D
2.35×D
500×
where D is the diameter of the telescope’s aperture (in mm).
10. Angular size units
1° = 60 arc-minutes, denoted 60′
1′ = 60 arc-seconds, denoted 60″
1 radian = 57.2957795 deg
= 3437.74677′
= 206264.806″
11. Speed of light
186,000 miles per second (300,000 km/s) = 6 trillion miles per year traveled
(9.6 trillion km)
12. Solar System distances from Earth (average)
Sun
Moon
Mars
Jupiter
93 million miles (150 million km)
253,000 miles (405,000 km)
50 million miles (75 million km)
400 million miles (650 million km)
Formulas
187
Saturn
800 million miles (1.3 billion km)
Ceres
160 million miles (256 million km)
International Space Station 240 miles (380 km)
13. How far can you see?
Because light travels 6 trillion miles (9.6 trillion km) each year [= 1 light-year
(LY)], get your calculator out for these objects.
The Pleiades M45
The Dumbbell Nebula M27
The Orion Nebula M42, M43
The Ring Nebula M57
The Crab Nebula M1
Globular Star Cluster M13
The Andromeda Galaxy M31
The Whirlpool Galaxy M51
Stars within the Milky Way Galaxy
Messier objects
Other galaxies
380 LYs
1250 LYs
1600 LYs
2300 LYs
6300 LYs
25,000 LYs
2.9 million LYs
37 million LYs
Thousands of LYs
The most distant Messier objects
= 60 million LYs
Hundreds of millions of LYs
Index
Accessories, 43–51
Aggressiveness, of an
autoguider, setting, 62
Alps, Caucasus mountains of
the Moon, image of, 85
Apennine mountains, image
of, 91
Aperture mask, homemade,
49
Asteroids
—76694
CCDSoft screen capture of,
165
TheSky screen capture of,
164
—determining the axial
rotation period of, 166
Astroart
—blink function of, 163
—deconvolution filters for
sharpening, 76
—for image processing,
35–36
after stacking multiple
images, 75
—initializing, 58
—variables selectable in, 62
Astrometry, minor body,
161–66
Astronomical Image
Processing (AIP), handbook
and software for, 36
Astronomik equipment
—filter holder, 58
—LRGB filters, 44
—Profi-H␣ filter, 43
Astronomy, viii, 159
Astrophotos
—collection of, 81–156
—processing of, 69–80
Astro Pier, in a Home Dome
observatory, 26–27
At Home in a Dome
(handbook), 24
Atmospheric extinction,
correcting for, in color
balancing, 78
Auriga
—emission nebula in, image
of, 107–8
—Open Star Cluster M37 in,
image of, 150
Autoguider
—camera as, 36–42
—STV
effect of skyglow on settings,
61–62
initializing settings for each
session, 57–58
Background glow, sources of,
2–4
Barlow lens
—for camcorder imaging, 51
—for increasing magnification,
43
Bell Laboratories,
charge-coupled device
camera development, 20
Bias frame, defined, 64
Binning, defined, 56
Blackeye Galaxy, M64, image
of, 139
Blue bloat, of an achromat, 15
Bortle Scale, rating of the
author’s imaging site, vii
Brightness, sky, 1–2
Bubble Nebula, NGC 7635
—images of, 117, 118
—with Open Star Cluster M52,
image of, 121
Cables, connecting the
computer with the telescope
and observatory computer,
32–34
Calibration
—of images, 71
—of an STV camera, 38, 42
routine for, 58
California Nebula, NGC 1499,
image of, 120, 122
Camcorder, ToUcam Pro
PCVC740K, 51
Cameras
—charge-coupled device,
20–24
—Starlight Xpress HX916,
21–22
—STV, from Santa Barbara
Instrument Group, 36–42
Canadian Meteorological
Center, forecasts designed
for astronomers, 55
Cassiopeia, open star cluster
in
—NGC 457, image of, 155
—NGC 663, image of, 146, 156
Catadioptric design, LX200
Schmidt-Cassegrain
telescope, 12–13
Caucasus mountains of the
Moon, image of, 91
CCD (charge-coupled device)
array, Sony ICX085AL, 22
CCD (charge-coupled device)
imager, xi. See also Cameras
CCDSoft
—image of galaxy NGC3432,
showing minor planet 76694,
165
—inventory of stars from, 163
Choosing and Using a
Schmidt-Cassegrain
Telescope (Mollise), 13
Christmas Tree Cluster, image
of, 106, 108
Cirrus Nebula, northwest part,
image of, 116
Clavius crater
—image of, 84, 89
—lunar terminator passing
near, image of, 82, 85
Clear Sky Clock site, for
planning imaging, 55
Cloud cover, effect on imaging,
56
Cocoon Nebula, IC 5146,
images of, 111
189
190
CCD Astrophotography: High Quality Imaging from the Suburbs
Collimation, need for
checking, 12
Color balancing, 78
Color images, processing, 77–80
Combining, exposure times,
72–73
Comets
—C/2001 Q4, image of, 103
—C/2004 F4, image of, 102
—C/2004 Q2, image of, 102
Campanus Rima, image of, 87
Computer, connection to the
telescope and observatory
computer, 31–34
Cone Nebula, with Christmas
Tree Cluster, image of, 106,
108
Consumer Reports, on photo
papers, 158
Cooling, thermoelectric, 36, 38
Copernicus crater, image of, 88
Corel Photo Paint, exporting
an Astroart image to, 76
Cosmos (Sagan), 31
Crab Nebula, M1, image of, 125
Crescent Nebula, NGC 6888,
image of, 122
Cygnus, open star cluster in,
NGC 6819, 148
Cyrillus crater, image of, 82
Dark frame, for correcting for
thermal noise, 64–65
Darkness, defined ideally, 56
Deconvolution, as a
sharpening filter, 76
Disks, CD-R, for a single
night’s images, 157
Dome-Dial, for monitoring
and displaying azimuth
direction of the observatory
dome, 27
Dome-Trak, link between the
telescope and dome slot
position, 27
Drift alignment, defined, 55
Drift Method, for checking
polar alignment, 12
Dumbbell Nebula, M27, image
of, 109–10, 126
Electricity, providing for an
observatory, 31
Emission Nebula
—IC 1795, image of, 119
—IC 410, in Auriga, image of,
107–8
Emission Nebula (continued)
—IC 443, image of, 124
—IC 1795, filtered composite
image of, 7
—NGC 1893, image of, 119
Ephemeris positions, for
asteroids and comets,
download of, 34
Equipment, 9–53
—battery backup, Belkin APC,
31
—computer monitor,
calibration of, 158
—computer operating system,
32
—electric focuser, 13
—eyepieces, from Meade
Instruments Corporation,
43
—optimization of, 56
—printers, Hewlett Packard
Photosmart 1115 Inkjet, 81
—repair services,
TelescopeService.com, 32
—sources
Celestron, Inc., focal
reducer, field flattener, 49
Jim’s Mobile, Inc., 13, 45
Kendrick Astro Instruments,
Inc., 45
Meade Instruments
Corporation, 44, 49
Oceanside Photo and
Telescope (OPT), 11
Santa Barbara Instrument
Group (SBIG), 36
Technical Innovations, Inc.,
for an observatory, 24
—See also Cameras; CCD
(charge-coupled device);
Telescopes
Eyepieces, range of sizes, 43
Files (continued)
—JPEG, 36
for posting images on a
Web site, 159
for saving images, 80,
157–58
Filters
—Astonomik, 43–44
—Astroart, Lucy-Richardson
and Maximum Entropy for
deconvolution, 76
—Astronomik, 7
—Digital Development Process
(DDP), 75
—hydrogen alpha, blocking
skyglow with, 7
—light-pollution-rejection, 5–7
Flame Nebula, NGC 2024,
image of, 104–5, 120
Flaming Star Nebula, IC 405,
image of, 106, 125
Flat-field frame, 65–66
Flexible image transport
system (FITS) images, 36
Floating-point math, for
summing to combine
images, 72
Focal reducer/field flattener,
49, 51
—for guiding, 57–58
Focuser
—electric, JMI NGF-S, 45
—manual, Crayford, on the
Stellarvue refractor, 58–59
Focusing, electric control of, 13
Focus mask, Hartmann, 46
Formulas, 181–83
Foxhead star cluster, NGC
6819, image of, 148
Full-width half-maximum
(Fwhm), measure of focus,
59
Field of view (FOV), wide,
using a reducer/field
flattener, 49, 51
Files
—Audio Video Interleave
(AVI), size of, 51
—BMP, for saving images, 36,
76, 81, 157–58
—FITS, to export to Corel
Photo Paint, 76
—FTP (File Transfer Protocol),
for uploading to an online
photo printing service,
158–59
Galaxies
—images of, 133–44
—NGC 3432
from CCDSoft, showing
Asteroid 76694, 165
raw image of, 163
from TheSky, showing
Asteroid 76694, 164
—NGC 3185, NGC 3189, NGC
3187, and MCG 4-24-22,
image of, 137
—UGC 4042, UGC 4039, CGCG
148-33, and UGC 4032,
image of, 136
Index
Gamma Cygni (Sadr), image
of, 113
Ganymede, with Jupiter and Io,
image of, 92
Gibbous Moon, image of, 83
Glare, reducing on the
telescope and camera, 5
Globular Star Cluster
—M3, image of, 130, 133
—M5, image of, 130
—M13, image of, 131–32
—M22, image of, 132
—M71, image of, 129
Globular star clusters, images
of, 129–33
Glossary, 171–80
Gradients, removing with
Astroart Gradient Removal
plug-in, 75
Gralak, Ray, freeware for
combining images, 73
Great Andromeda Galaxy,
M31, image of, 134
Great Orion Nebula, M42,
image of, 127–28
Greiner, R. A., information
from the works of, 11
Guide Star Catalog (GSC), 36
—matching images to, 164
Hartmann focus mask, 46
Hercules Globular Star Cluster
M13, images of, 131–32
Hesiodus crater, image of, 86
Hesiodus Rima, image of, 86
Hippalus Rima, image of, 87
Hipparcos/Tycho stellar
catalog, 164
Horsehead Nebula, B33/IC434
—with Flame Nebula, images
of, 104–5
—image of, 107, 112, 123
Humidity, effect on imaging, 5,
57
Image reduction, defined, 71
Images
—of minor bodies, process of
obtaining, 162–63
—oversampled and
undersampled, 23
—software for processing,
35–36
Image scale, defined, 56
Imaging, a night of, 55–67
Infrared detectors, for tracking
the dome slot opening, 62
191
Installation, of a prefabricated
fiberglass observatory,
29–31
Integration time
—effect of filters on, 6
—and magnitude of sky
brightness, 1–2
International Astronomical
Union, Committee for
Small-Body Nomenclature,
166
International Dark Sky
Association (IDA), 2
Internet sites
—iphotoshop.com, for
printing images, 158–59
—www.cleardarksky.com,
weather information, 55
—See also Website
Io
—with Jupiter and Ganymede,
image of, 92
—with Jupiter and Great Red
Spot, image of, 97
Jupiter
—blue/green festoons in the
image of, 97
—and Great Red Spot
image of, 92
with Io and Ganymede’s
shadow, images of, 93–94
with Io, image of, 94, 97
—image of, 91
—with Io, Europa and
Ganymede, montage, 95–96
—with Io and Ganymede,
image of, 92
Kendrick dew heater, 45–46
Lace-Work Nebula, and Cirrus
Nebula, images of, 116
Lens, mirror-lens design,
focusing, 13
Leo Triplet Galaxies, M65, M66
and NGC 3628, image of, 141
Light box, for flat-field control,
66–67
Lightning, effect on
equipment, 31–32
Light pollution
—challenge of imaging the sky
under, 1–7
—levels of, map of Europe, 3
Lilius crater, image of, 88
Lincoln Near-Earth Asteroid
Research, discovery of
comets and asteroids by, 165
Losmandy ring and dovetail
set, for attaching a
piggyback refractor to an
LX200, 44
Luminance layering, for color
images, 77–78
Mare Crisium, image of, 90
Mare Nectaris, image of, 87
Mars, montage, 100–101
Max Correction, defined, 62
Meade 10-in. LX200 telescope,
with an HX916 camera,
resolution of, 56
Meade Superwedge,
modification of, 17–19
Median combination
—of light frames, dark frames
and bias frames, 72
—to stack images containing
artifacts, 73
Messier, Charles, discovery of
the Dumbbell Nebula M27,
110
Minor Planet Center (MPC),
161
Minor Planet Circulars, 161
Mirror-lock bolt, 13
Mollise, Rod, 13
Moon
—craters of, images of, 84, 89
—full, image of, 86
Moon filter, ND-96, Meade
Instrument Corporation, 44
Near Earth Asteroid Tracking,
discovery of comets and
asteroids by, 165
Near Earth Orbit (NEO),
refining the orbits of, 166
Nebula Complex, IC1396,
image of, 117
Nebulae, images of, 104–29
Needle Galaxy, IC2233, with
Bear Paw and Spiral Galaxy
NGC 2537A, image of, 142
Network Nebula, NGC6992,
image of, 114
The New CCD Astronomy
(Wodaski), 69
New Moon, imaging during, to
reduce skyglow, 5
Night sky, virtual, display on a
PC desktop, 34–35
192
CCD Astrophotography: High Quality Imaging from the Suburbs
Niobe asteroid 71, image of, 104
Noise
—imaging frames for
managing, 62–63
—reducing by combining
images, 72–75
North American Nebula, NGC
7000, image of, 112
Nyquist sampling theory, on
ideal telescope/camera
resolution, 56
Observatory, 24–32
—fiberglass, vii
Observatory designation, by
the Minor Planet Center, 161
Open Star Clusters
—images of, 144–56
—M34, image of, 148
—M35, with NGC 2158, image
of, 149
—M36, image of, 149
—M37, image of, 150
—M38, with NGC 1907, image
of, 150
—M39, image of, 151
—M44, image of, 151
—M46, with Planetary Nebula
NGC 2438, image of, 152
—M47, with NGC 2423, image
of, 152
—M50, image of, 153
—M52
with Bubble Nebula, image
of, 121
image of, 118
—M67, image of, 153
—M103, image of, 145
—NGC 457, image of, 155
—NGC 663, image of, 146, 156
—NGC 743, image of, 147
—NGC 869 with NGC 884,
image of, 145, 154
—NGC 884 with NGC 869,
image of, 145, 154
—NGC 1528, image of, 146
—NGC 1582, image of, 147
—NGC 1907 with M38, image
of, 150
—NGC 1931, image of, 154
—NGC 2158 with M35, image
of, 149
—NGC 6705, image of, 144
—NGC 6819, image of, 148
—NGC 6910, image with Sadr
and surrounding nebulae,
113
Open Star Clusters (continued)
—NGC 7209, image of, 155
Optical vignetting, example, 71
Orion, M42, Great Nebula in,
image of, 114
Orion accessory case, 45
Pac Man Nebula, NGC 281,
image of, 115
Pelican Nebula, IC5067-70,
composite image of, 112
Periodic error correction
training drive worm gear, 12
Perseus
—Double Cluster in, image of,
154
—open star cluster in, NGC
1528, 146
Photometry, for determining
axial rotation period of an
asteroid, 166
Pickerings Triangular Wisp
(Veil Complex NGC 6960),
image of, 110
Piers
—footing for the observatory,
28–30
—Le Sueur Astro Pier, 19–20
in a Home Dome, 26–27
Plato crater, image of, 90
—testing resolution of optics
with, 83
Pointing accuracy, defined, 12
Point spread function (PSF),
deconvolution using, 76
Polar alignment
—defined, 12
—maintaining, 55
Praesepe, Open Star Cluster
M44, image of, 151
Printers, Hewlett-Packard
inkjet, for printing digitized
images, 158
Printing, by on-line services,
158
Processing, software for, Corel
Photo Paint-8, 81
Procyon, image of, 59
Quantum efficiency (QE), of a
charge-coupled device
camera, 23
References, with Web
addresses, 167–70
Refractor telescopes,
piggybacked, reasons for
needing, 13–16
Reticle, for refining polar
alignment, 49
Ring Nebula, M57
—image of, 109
—wide-field image of, 129
Rosette Nebula
—focus on a star in, 60
—heart of, image using a
Stellarvue Nighthawk at f/6,
121
—image using an Astronomik
13-nm Ha filter, 5
—image using a Takahashi FS
60C at f/6, 105
—screen capture image using
Sigma pre-beta 11, 74
Running Man Nebula, NGC
1977, image of, 127
Sagan, Carl, v, 31
Santa Barbara Instrument
Group (SBIG), STV camera
from, 36–42
Saturn
—images of, 98–99
—stacked image, 79
Scheiner disk, for refining
focus, 46
Sculptor Galaxy, NGC 253,
image of, 144
Seeing
—considering in setting the
guider, 62
—defined for imaging, 56
Sharpening, with filters,
75–77
Signal-to-noise ratio (S/N), 1
—of combined images, 6–7
—conditions for reducing, 70
Skyglow
—correcting for, in RGB
exposures, 78–79
—effect on imaging, 1
Sky & Telescope, viii, 159
Software
—AIP4WIN, for astronomical
image processing, 36
Calibrate routine of, 71–72
combining multiple images
using, 74–75
imaging minor planets
using, 163
—to capture camcorder
images, 51–52
Index
Software (continued)
—CCDSoft, screen capture
showing galaxy NGC3432
and minor planet 76694,
165
—for a charge-coupled device
camera, 21–22
—Find Orb, to confirm
identification of a minor
body, 165–66
—freeware
Atomic Clock Sync, 57
RealVNC Viewer, 34, 57
Sigma pre-beta 11, for
combining images, 73–75
—Image Link, for pattern
recognition to identify stars,
164
—for image processing, 35–36
—K3CCD Tools, for capturing
camcorder images, 51
—for observing and telescope
control, 34–35
—Pictor, 11
—RegiStax, for processing
camcorder frames, 52
—TheSky, 4, 11, 57
for imaging minor planets,
163
for locating minor planets,
162
for observing, 32, 34–35
Solar system, images of,
82–104
Sombrero Galaxy, M104, image
of, 139
Spacecraft, imaging from
Voyager, with a
charge-coupled device
camera, 20
Spectral response curve of the
Sony ICX085AL chip, 23
Spiral Galaxy
—M33, image of, 133
—M65, dark frame-reduced
image, with and without
flat-field-reduced image, 66
193
Spiral Galaxy (continued)
—M74, image of, 140
—M106, image of, 134
—NGC 891, edge-on images of,
140–41
—NGC 2543, image of, 135,
143
—NGC 2862, image of, 138
—NGC 2903, image of, 135
—NGC 2964, image of, 138
—NGC 2968, image of, 138
—NGC 3432, barred, image of,
137
—UGC 3587, image of, 136
Stacking methods, for image
processing, 72
Standards, for Minor Planet
Center reports, 161
Star count (ADU Values),
maximizing, 59
Startup, procedures for
imaging from an
observatory, 57
Stellarvue refractor, with an
HX916 camera, resolution
of, 56
Storage, of astrophotos, 157–59
Sunspot Complex 484, image
of, 99–100
Superwedge, 17–20
Surveillance camera, for
monitoring equipment
during remote operation, 52
Target
—locating, automatic, 13
—selecting, 60–61
Technical Innovations, Inc.,
fiberglass observatory
source, 24
Telescopes
—Meade 10-in. LX200 f/10
classic, 12–13
—Meade 10-in. LX200
Schmidt-Cassegrain, vii, 10
control with TheSky, 34
Telescopes (continued)
—selecting, 9–10
—Stellarvue Nighthawk with
Crayford Focuser,
piggybacked refractor,
13–16
—Takahashi FS 60-C
apochromat, 16
—Tasco refractor, vii
Temperature, effect of changes
on primary mirrors, 57
Theophilus crater, image of, 82
TheSky. See Software
Timing of imaging, to reduce
skyglow, 4–5
Tracking by an STV camera,
42
Transparency, atmospheric,
defined, 56
Turbulence, atmospheric,
effect on seeing, 56
Two-line elements (TLEs), for
locating satellites, 34
Vallis Alpes, image of, 90
Weather
—effect on imaging, 56
—local, tracking, 55
Web addresses, 167–70
Website
—DarkSky, of the
International Dark Sky
Association, 2
—designing, 159
Whirlpool Galaxy, M51,
images of, 142–43
Wild Duck Cluster, NGC 6705,
image of, 144
Wind speed, effect on imaging,
56–57
Zenithal Limiting Magnitude,
patterns of values for the
United States, map, 2
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