How to buy your first telescope

How to buy your first telescope
Sponsored by
Telescopes 101
Buying your first telescope is a big step, especially if you’re not
sure what all those terms mean. So, to help you understand
what to look for in a quality telescope, the editors of Astronomy
magazine answer 11 of the most-asked questions.
know telescopes make
appear bigger, but
exactly do they do?
A telescope’s purpose is to collect light.
This property lets you observe objects
much fainter than you can see with your
eyes alone. Italian astronomer Galileo Galilei said it best when he declared that his
telescopes “revealed the invisible.”
Will my telescope be complete,
or will I need additional items
to make it work?
Most Celestron telescopes are complete
systems, ready for the sky as soon as you
unpack and assemble them. A few models
are “optical-tube assembly only.” This
means all you’re buying is the optics in the
tube with no tripod or accessories.
high winds, but a poor mount will transfer
vibrations even in a light breeze. So, be sure
your scope sits on a high-quality mount.
To see objects
through your scope in
their normal orientation,
you’ll need an accessory
called an image erector.
in observing.
3 I’mWhatinterested
should I do first?
scope better
9 Isthana “go-to”
one without go-to?
Learn all you can about telescopes: what
types are available, the best accessories, and
what you’ll see through them. This publication is a good start because you’ll see a wide
range of options.
If a telescope interests you, visit www. to read more about it. You’ll
also find telescope reviews online at www. You’ll learn
what’s important to veteran observers when
they use a telescope. You’ll also get a feel for
mechanical quality, ease of use (including
portability), and extra features.
I buy binoculars
4 Should
before I buy a telescope?
No. The view through binoculars — especially near a city — won’t be what you
expect. They are, however, a valuable accessory at a dark site. Star clusters look great
through them, as do the Milky Way, meteor
trails, and the Moon. Learn more about
binoculars on page 11.
Why are objects through my
telescope upside-down?
Because of the way a telescope focuses light,
the top of what you’re looking at is at the
bottom as it enters the eyepiece, and viceversa. You can re-flip the image with an
accessory called an “image erector,” but
you’ll lose a bit of the object’s light. And for
faint sky objects, you want the maximum
amount of light possible to reach your eye.
Besides, there’s no up or down in space, and
with most objects, you won’t even know
they’re upside-down.
I use my telescope for
6 Can
views of earthly objects?
Absolutely! Many nighttime observers
(usually those with smaller telescopes) also
use their telescopes for bird-watching or
other daytime nature-watching activities.
Here’s where the image erector (see #5)
comes in most handy.
Your telescope also can give you great nature
views, like the one of this painted bunting, in
the daytime. Howard B. Cheek
Light rays
Astronomy: Roen Kelly
Any mirror (or lens)
twice as large as
another captures four
times as much light.
So, a 6-inch mirror
collects four times
the light as one 3
inches across.
To eye
focal length
focal length
Telescopes flip the view of your target, which doesn’t matter at
all if you’re looking at an object in space. Astronomy: Roen Kelly
Is there a way for me to
“test-drive” a telescope?
Yes. Look in your area for an astronomy
club and visit one of its meetings, which
usually occur monthly. There, you’ll find
others who enjoy the hobby and are willing
to share information and views through
their telescopes. At one of the club’s stargazing sessions, you’ll be able to look through
many different telescopes in a short period
and ask all the questions you like.
from quality optics,
what’s the most important
in a telescope system?
The mount, which is what the telescope’s
tube sits on. You can buy the finest optics
on the planet, but if you put them on a lowquality mount, you won’t be happy with
your system. No telescope can function in
Celestron’s Inspire 80AZ
is a complete package. It comes with the
telescope, tripod, eyepieces, and a lens cap
that doubles as a smartphone adapter for
capturing images. Celestron
A local astronomy club’s observing session, or
a star party like the one pictured here, is a great
place to “test-drive” a telescope. Celestron
Celestron’s FirstScope
is an ideal “grab and go”
telescope: It’s small, light,
and sets up on any level
surface. Celestron
Yes. A go-to telescope is one with a motor
or motors controlled by a built-in computer. Once set up for an evening’s observing, a go-to scope will save you lots of time
by moving to any sky object you select and
then tracking it. Even experienced observers prefer go-to scopes because they leave
more time to observe the sky.
NexStar SLT
offer go-to
technology at an
entry-level price.
10 IfdoesI useit myneedtelescope
Only if it has a motorized drive. In most
cases, telescope drives use direct current,
which means you can use batteries (including the one in your car). Adapters available
from the manufacturer will let
you plug your scope into an
electrical outlet.
the best
telescope for me?
It’s the one you’ll use the
most. If it takes an hour to
set up a scope, or if your
scope is large, heavy, and
difficult to move, you might
observe only a handful of times each
year. If, on the other hand, your scope is
quick to set up, you may use it several times
each week. A small telescope that’s used a
lot beats a big scope collecting dust in a
closet every time.
A go-to mount, like the one
included with Celestron’s
NexStar Evolution 8 telescope,
makes observing easy! A 10
hour internal battery plus
wireless telescope control via
WiFi makes the Evolution a
popular choice. Celestron
This adapter will let you
power your scope from a
car’s cigarette lighter. Celestron
Sponsored by Celestron
All about refractors
here light is concerned, the word
refract means “to bend.” A refracting telescope (usually called a
refractor) does this with a carefully made
lens system. If the surfaces of the lenses
have the proper shape, the light will come
to a focus. Placing an eyepiece at that “focal
point” will let you see what you have
pointed the telescope at.
Dutch eyeglass-maker Hans Lipperhey
made the first telescope (a refractor) in
1608. His patent application described “an
instrument for seeing faraway things as
though nearby.” The tube magnified objects
about three times. Italian inventor Galileo
Galilei was the first to use the telescope to
study celestial objects, and what he saw
revolutionized astronomy forever.
Two words you’ll see when reading
about today’s refractors are achromat and
apochromat. Each is a lens system combining different types of glass. Achromat
means “not color dependent.” Such a lens
has two pieces of glass and does a pretty
good job of bringing all colors of
light to the same focus.
Apochromatic lenses are also
available. They are the top of the
line, and their front lenses combine up to four pieces of glass.
Into the 1960s, refractors topped
all telescopes in terms of numbers sold.
Then, as manufacturers began making large
scopes of other designs, sales of traditional
refractors fell. In recent years, however,
refractor sales have made a dramatic comeback due to several factors you may want to
consider when you buy a telescope.
First, the overall quality of refractors has
risen dramatically. Second, better lenses
have made shorter tubes possible. Finally,
lighter materials mean small models now
transport more easily. Not only does this
simplify travel to your favorite viewing site,
but it also helps you decide whether or not
to set your scope up in the backyard for a
quick view of the Moon or Jupiter.
produce images.
• Refractors require the least
maintenance of all telescopes.
• Many small refractors are light
enough to mount on a sturdy
camera tripod, making them the
ultimate grab-and-go scopes.
Lens shade
Telescope tube
A refractor uses a lens (a combination of two to
four polished glass pieces) to bring light to a
focus. Astronomy: Roen Kelly, after Celestron
Celestron’s PowerSeeker
60AZ is an example of a
small, low-priced refractor.
It has a 2.4-inch lens, sits
on a simple mount, and
produces right-side-up
images with the supplied
diagonal. Celestron
All about reflectors
cottish astronomer James Gregory
invented the reflecting telescope and
published a description of it in 1663.
Although astronomers and historians give
him credit for the invention, Gregory never
actually made the telescope.
English mathematician Sir Isaac Newton
constructed the first working reflecting
telescope in 1668. It had a mirror 1.3 inches
across and a tube 6 inches long.
Today, every “Newtonian” reflector contains two mirrors — a large curved one
called the “primary” at the bottom of the
tube, and a small, flat “secondary” near the
top. Light enters, travels down the tube, hits
the primary, and reflects to the secondary.
That mirror then reflects it to the eyepiece.
Through half of the 20th century, amateurs built their own reflectors. Now manufacturers offer high-quality models, and
they’re a bargain. Overall, reflectors are
the least expensive telescopes, so if
budget is a factor, you’ll want to look
into buying a small reflector.
But the biggest amateur scopes
are also reflectors. So, if
moving a large, heavy
“light bucket” isn’t a
problem, maybe a
12-inch or bigger reflector is
in your future.
• Reflectors use a system of mirrors to
produce images.
• A reflecting telescope offers the best
“size per dollar” ratio.
• The largest amateur telescopes
are reflectors.
Primary mirror
Secondary mirror
Telescope tube
Secondary mirror holder
A reflector uses a curved mirror to focus light and a small, flat mirror to
reflect it to the eyepiece. Astronomy: Roen Kelly, after Celestron
Celestron’s AstroFi 130mm Newtonian
is a 5-inch reflector on a computerized
mount controlled via WiFi. No hand
control needed! Celestron
SkyProdigy 130
is a reflector that
contains a 5.1inch primary
mirror. Celestron
Celestron’s AstroMaster
130EQ is a 5.1-inch
reflector on an equatorial
mount. Celestron
• Reflecting telescopes show no excess color. That means you won’t see color
fringes around even the brightest objects.
• Inch for inch, reflectors are less expensive than other telescope types. When
trast better. Observers of planets and double stars (who need high contrast to
resolve small details) say that refractors are best for such objects.
• Refractors are low maintenance. Lenses never require recoating like mirrors eventually do. Also, a lens usually doesn’t need adjustment — what telescope-makers call
“collimation.” The lens does not get out of alignment unless the scope encounters a
major trauma like falling onto a hard surface.
• Because a refractor has a closed tube, it requires some time to adjust to the outside
temperature when moved from a warmer or cooler house. Today’s thin-walled aluminum tubes conduct heat well, so they have reduced the cool-down time a lot.
But you still have to take it into account.
• Refractors use a lens system to
• Nothing blocks any of the light passing through the lens, which makes image con-
NexStar 102SLT
combines a 4-inch
refractor with a
mount. Celestron
working with a mirror, manufacturers have to polish only one surface. An apochromatic lens has between four and eight surfaces, plus you’re looking through
the lenses so the glass has to be defect-free. All of this makes such lenses more
expensive. Telescopes with apertures of more than 6 inches, with few exceptions,
are all reflectors or compound telescopes (see page 6).
• The placement of the secondary mirror creates an obstruction that scatters a tiny
amount of light from bright areas into darker ones. Unless you’re looking at a
planet or bright nebula under high magnification, you’ll never notice this.
• Newtonian reflectors suffer from “coma,” a defect that causes stars at the very
edge of the field of view to look long and thin like a comet. Observers generally
compensate for this by placing all targets at the center of the field.
• Because of how the mirror attaches to the tube, a reflector is sensitive to bumping
or jostling when transported. To be sure all is well, many skygazers collimate their
telescopes (adjust the mirrors) before each observing session.
Sponsored by Celestron
All about compound telescopes
• Compound telescopes employ a
ith regard to telescopes, “catadioptric” means “due to both the
reflection and refraction of light.”
These instruments also are known as “compound” telescopes and are hybrids that
have a mix of refractor and reflector elements in their design.
German astronomer Bernhard Schmidt
made the first compound telescope in 1930.
The Schmidt telescope had a spherical primary mirror at the back of the telescope
and a glass corrector plate in the front.
The Schmidt telescope was the precursor of today’s most popular design, the
Schmidt-Cassegrain telescope, or SCT. It
also incorporated elements by French professor Laurent Cassegrain. In the SCT, light
enters the tube through a corrector plate
and then hits the primary mirror at the
tube’s base, which reflects the light to a secondary mirror mounted on the corrector.
The secondary reflects light through a hole
in the primary mirror to the eyepiece,
which sits at the back of the scope.
combination of lenses and mirrors to
produce images.
• They have the most compact design.
• Manufacturers usually sell them as
complete systems.
Celestron’s NexStar
6SE utilizes a type of
compound telescope
called a SchmidtCassegrain. Celestron
In the 1960s, amateur astronomer John
Dobson invented a type of alt-azimuth
mount that now bears his name. The Dobsonian mount is the least expensive mount,
and manufacturers always combine it with
a reflector. Because the tube sits loosely in
the mount, you can carry the two parts
quite easily. But these scopes also can be
large. Every amateur telescope that has a
mirror more than 16 inches across sits in a
Dobsonian mount.
Primary mirror
Telescope tube
Alt-azimuth mounts
• A mount holds a telescope and also
Equatorial mounts
defines how it moves.
If Earth did not move, a non-motorized
alt-azimuth mount would be all that any of
us would ever need. But our planet does
spin, and we must deal with it. The third
type of mount is the equatorial mount.
German optician Joseph von Fraunhofer
invented it in the early 19th century to
track the stars. He aligned one of the
mount’s axes parallel to Earth’s axis and
moved the mount (with a weight-driven
clock drive) at the same rate as our planet’s
spin. By doing so, the telescope follows the
stars as they move through the sky. Today,
many equatorial mounts incorporate a
motor to move them.
• It is every bit as important as the
telescope’s optical tube.
• You can enhance your observing
with a go-to mount.
Go-to mounts
A recent development is the go-to mount.
To create this, manufacturers attach motors
to both the altitude and azimuth axes. The
motors also connect to an onboard computer. Once you run through a simple setup
procedure, the go-to drive will find and
then track your celestial target.
Mounts using this system are highly
accurate. Once the drive locates an object,
it will follow it as it moves across the sky
without you moving the telescope. Most
go-to scopes manufactured today have
large databases with thousands of objects.
Dobsonian mounts
AstroMaster Tripod
is a simple alt-azimuth
assembly on which
you can mount
binoculars or a small
telescope. Celestron
Secondary mirror
Focus knob
Corrector plate
To North Celestial Pole
A compound telescope combines a front lens with mirrors to focus light. This diagram shows a
Schmidt-Cassegrain telescope. Astronomy: Roen Kelly, after Celestron
• The number-one advantage of a compound telescope is its compact design. Such
Altitude axis
Polar axis
Altitude axis
Azimuth motion
instruments are often only one-quarter as long as comparably sized reflectors and
much shorter than refractors with half their aperture. This feature makes the compound telescope a great grab-and-go instrument.
side temperature, therefore, takes longer than with an open-tube reflector with the
same size mirror. To speed cooling, Celestron installs filtered cooling vents behind
the primary mirror of its top-end Schmidt-Cassegrain telescopes.
Celestron’s specialty Dobsonian
telescopes for Astronomer’s Without
Borders combines a Newtonian
reflector with an easy-to-use
Dobsonian mount all while
supporting a good cause. Celestron
Fixed base
• Like refractors, compound telescopes also have a closed tube. Adjusting to the outCelestron
In 1970, Celestron began making a
telescope that took amateur astronomers by storm: the Celestron 8, or the
C8 as observers soon called it. The
introduction of this scope started a
revolution. The orange-tubed
Celestron 8 SCT had many advantages — 8 inches of aperture, light
weight, better portability than any
8-inch reflector sold at the time, and
an f/10 optical system, which provided good magnification. A range of
ready-to-use accessories made celestial photography simple and popular.
The complete system included a
wedge users adjusted to their latitude
and a sturdy,
folding tripod.
Celestron based
several of its
current telescopes on this
proven design,
including the
CGEM, Edge HD,
CPC, NexStar SE,
and Advanced
Celestron’s original C8
Series lines.
e call these instruments “telescopes,” but the phrase “optical
tube on a mount” also works. In
fact, it points out that half of any telescope
system is its mount.
An unstable mount will not let even the
best telescope deliver quality images. If the
mount is too light, wind will be only one of
your enemies. Your images will “bounce”
even when you are focusing.
An alt-azimuth mount is the simplest type
of telescope mount. The name is a combination of “altitude” and “azimuth.” This
type of mount moves up and down (altitude), and left and right (azimuth).
The Advanced VX 8”
EdgeHD features
Celestron’s highest quality
optical technology on a
solid equatorial mount
that makes it the perfect
first choice for any aspiring
All about mounts and drives
Azimuth axis
Altitude-Azimuth mount
Dobsonian mount
Equatorial mount
The most popular amateur telescope mounts are shown in this illustration. Astronomy: Roen Kelly
Sponsored by Celestron
Which accessories are right for you?
Enhance your observing fun by adding
some well-thought-out extras.
Star diagonals
Finder scopes
The world’s best telescope is useless if you can’t find anything with
it. Its high magnification limits the field of view. Even with a go-to
drive, you’ll need a quality low-power finder scope. Most are tubes
you view straight through. They flip the image but let you look
toward the object, a position that’s intuitive for most people.
Your finder should have a front lens at least 2 inches (50mm) in
diameter. That size will let enough light in so you won’t get frustrated trying to find faint objects. The finder’s magnification also
should be between 7x and 9x (see page 10).
Once you install your finder scope, align it with your telescope.
Do this when it’s still light outside using a distant object like the
top of a telephone pole. It’s easier then because the objects you’ll
use to align your finder won’t be moving (like the stars do).
This small finder
scope doesn’t
magnify. Rather, it
projects a red dot
onto a transparent
screen. Celestron
If you plan to use Astronomy
magazine or a star chart while
observing at night, you’ll need
light. Red light is best because
it affects your night vision (the way your
eyes adapt to the dark) least. But a bright
light (even red) means you’ll see less
through the telescope because your eyes will
have to re-adapt to the darkness. So, the best
flashlight is one that lets you
adjust its brightness.
If you observe from a location
with alternating-current power,
consider yourself lucky. The rest
of us need some form of portable
power. With the right adapter,
you can use your car’s battery.
Another option is a dedicated
power supply. Celestron’s PowerTank 17, for example, has
plenty of power for several allnight sessions. It also includes a
17 amp-hour battery, two 12-volt
DC car-style outlets, an AM/FM
radio, a siren, a removable redfiltered flashlight, and a white
Align your finder scope before each observing session while
it’s still light outside. Here’s how:
• If your telescope has a motorized drive, turn it off.
• Insert a low-power eyepiece (the one with the largest
number printed on its barrel).
• Loosen your drive’s motion-control locks.
• Move your telescope until you center a distant object (the
light on a transmission tower, a building, etc.). Focus your
scope on the object.
A red flashlight like
this one is a great
accessory to preserve
your night vision when
you’re out observing.
Celestron’s PowerTank
Lithium packs 10 hours of
power to your computerized
telescope with a red/white LED
light and two USB ports to
charge your personal
electronics. Celestron
This handy device will let you mount your
binoculars onto a standard camera tripod.
This offers two advantages. First, it
relieves you of holding your binoculars for long periods. Second, you
can show someone else what
you’re looking at without giving
any directions except “look
through here.”
bracket and then (without moving the main scope) position the finder scope so the object you centered in your
scope also is centered in your finder.
• Lock your finder scope into position.
• For higher precision, replace the low-power eyepiece in
your telescope with a high-magnification one, and then
realign your finder scope.
As you observe through your telescope, filters will help you see
more details. Astronomical filters come in two main varieties:
color, which enhance viewing the planets, and light-pollution
reduction (LPR) filters, which
reduce man-made light so you
can see nebulae better. All filters
screw into the threads manufacturers put in the barrels of eyepieces.
StarSense AutoAlign Accessory – Using a computerized telescope often required a lengthy alignment
process of finding and centering at least two
bright stars in the telescope’s eyepiece.
StarSense automatically aligns itself with
minimal user input. Just enter your time, date,
and location and in about three minutes, it has
gathered enough information to triangulate its
position and align itself. Then, press the Sky Tour
button: StarSense will automatically slew to all
the best stars, planets and galaxies.
Color filters
Color filters made for astronomy
improve the view through even a
low-quality telescope because
Celestron’s Eyepiece Filter Set
they boost the contrast between
contains red, blue, and yellow
areas on a planet’s surface or in its filters that bring out details
atmosphere that have different
on the planets, and a neutral
colors. Manufacturers label color density filter for reducing the
Moon’s bright light. Celestron
filters along their edges, but you
can tell what light a filter lets
through either by looking at or through it. A red filter, for
example, looks red.
Color filters work better with larger telescopes because it’s all
about how much light is available. A bigger scope captures more
light. So, for example, a violet filter lets only 3 percent of the light
hitting it through. You’ll need a large scope to see details on any
object you view through this filter. If you have a small scope, try a
light blue filter, which lets 73 percent of the light through. Its effect
won’t be as dramatic as the darker filter’s, but the object you’re
observing will look a lot brighter.
Celestron’s FREE
SkyPortal app, for iOS
and Android devices
offers full telescope
control via WiFi for
computerized Celestron
telescopes with WiFi or
equipped with the
SkyPortal WiFi module
accessory. Celestron
Light pollution reduction (LPR) filters
Binocular tripod
• Lock your telescope’s motion controls.
• Loosen the screw locks on your finder scope’s mounting
Power supplies
Celestron’s Finderscope
Kit features a finder scope
with a 2-inch (50mm) front
lens and a magnification
of 9x. Celestron
A star diagonal
bends light 90°. This
accessory makes
observing more
comfortable. Celestron
Refractors usually need a star diagonal
because of their design. A star diagonal bends the light from your target
90° into the eyepiece. Without a star
diagonal, you’ll find yourself in some
awkward physical positions when
you’re observing objects high in the
sky. The star diagonal fits into the telescope’s focuser, and the eyepiece fits
into the star diagonal.
LPR filters work because many outdoor lights produce
only a few distinct colors (that blend to create white
or yellow light). For instance, a high-pressure
sodium-vapor streetlight shines mainly
yellow. Mercury-vapor lamps give off green and blue
light. LPR filters block those colors but allow others
But they’re not a cure-all. LPR filters do little to
reduce the impact of car headlights and incandesreduction filters
cent bulbs, which give off all visible colors. So you’ll
help you get
still need to pick your observing site with some
better views of
nebulae. Celestron
StarSafari app
upgrade path retains
all “Celestron only”
functionality with an
expanded database
plus more! Celestron
SkyPortal App –
Developed in collaboration with the experts at
SkySafari, SkyPortal features a database of more
than 100,000 celestial
objects. Plan your observing session before you set
up your telescope, viewing lunar automatically
aligns eclipses, planetary conjunctions, and
other your computerized notable events into
the future or into the past.
Optional SkySafari Upgrade – For the
largest object database, including asteroids,
comets, and satellites, upgrade to the hugely
expanded SkySafari Plus or SkySafari Pro
paid apps for iOS and Android. Like SkyPortal, Celestron’s proprietary telescope control
software is embedded within SkySafari. It
has all the “Celestron only” functions, including direct telescope alignment from
the app, SkyAlign, true mount
modeling using up to 10
alignment stars, and compatibility with Celestron’s
patented StarSense AutoAlign
accessory. No other combination
of app and mount hardware can
provide anything like this
astronomical experience.
Skyportal WiFi
Module, enables
SkyPortal WiFi Module Accessory – Align and conwireless telescope
trol your telescope wirelessly using your smart phone
control from your
or tablet and Celestron’s free SkyPortal app for iOS and
phone or tablet.
Android devices. Tap any celestial object you see in the Celestron
sky to identify it instantly. Tap again and your telescope slews to that object, centering it perfectly in the
eyepiece. As SkyPortal Wifi Modele slews your telescope to an object,
you can listen to hundreds of included audio descriptions on your
device, which explain history, mythology, and key features of the most
popular celestial objects.
Moon filters
Connect your
to a standard
camera tripod
with this
adapter. Celestron
automatically aligns
your computerized
Celestron telescope
with the night sky in
mere minutes for
the best observing
experience. Celestron
This specialty filter sometimes goes by the name “neutral density
filter.” It reduces the amount of light (by absorbing it) but doesn’t
filter or change any of the colors.
Neutral density filters let as much as 80 percent, and as little as
1 percent, of the light through. In general, lighter neutral density
filters are used for the planets and darker ones for the Moon, which
reflects much more of the Sun’s light.
Sponsored by Celestron
Understanding eyepieces
yepieces are like stereo equipment. You
want a sound system that faithfully
reproduces music as close to the original as possible. And yet, while listening to a
familiar piece of music, each of us perceives
something a little bit different about it. You
may hear some nuance meaningful to you
that I didn’t catch. The result is that we
don’t all end up with the same stereo equipment … or eyepieces.
Sometimes this is due to cost and the
quality of workmanship. The best eyepieces
contain multiple highly polished and
coated lenses made from exotic glass, so
they are not cheap. Coatings, by the way,
are ultra-thin layers that manufacturers
Celestron’s Eyepiece and Filter Kit contains
five eyepieces, a Barlow lens, six color filters,
and a Moon filter. Celestron
• Eyepieces change the magnification
of any telescope.
• They come in two sizes: 1¼" and 2".
• Their bodies show the focal lengths.
you actually see when you look through the
eyepiece. This number will change from
one telescope to the next.
High-quality eyepieces deliver highcontrast views and sharp images all the way
to the edge of the field of view.
21mm / 68°
Ultima Duo eyepiece
Celestron’s 40mm
Omni eyepiece
apply to lenses to reduce the amount of
stray light reflected and increase the
amount that passes through.
Some hobbyists find it tough to justify
spending as much on a few eyepieces as
they did on their telescope. Most amateur astronomers, however, look at the
investment over the long term. If you
upgrade your telescope, you don’t need
to change your eyepieces.
When choosing which eyepiece to
buy, consider its weight. Believe it or
not, some tip the scale at more than 2
pounds — as heavy as some binoculars.
If you purchase a small- or mediumsized telescope, you’ll want to choose
lighter eyepieces.
Another thing to keep in mind is
the eyepiece’s field of view. You’ll see
two numbers used: the apparent field
of view and the true field of view. The
apparent field of view of an eyepiece
just tells the angle of light that enters
the eyepiece. Eyepiece apparent fields range
from 25° to 84°. Much more important is
an eyepiece’s true field — the amount of sky
Barlow lenses
A Barlow lens is an optical accessory that
increases an eyepiece’s magnification. It
goes between the telescope’s focuser — or
the star diagonal if you’re using one — and
the eyepiece. Some Barlows magnify two
times (2x), some are 3x, and so on. So, as an
example, let’s say your 18mm eyepiece gives
a magnification (you’ll also hear this called
“power”) of 100x through your telescope. If
you insert a 2x Barlow, the magnification
will be 200x.
Roughly 50 years ago, when Barlow
lenses first appeared, they were simple units
using single lenses. They worked, but they
worsened the view. Today’s Barlows contain
high-quality coated lenses that transmit
nearly all of the light hitting them.
A Barlow lens can effectively double the
number of eyepieces in your set, if you
select your eyepieces with this in mind.
Here’s an example: Let’s say you have
40mm, 32mm, 12mm, and 9mm eyepieces
that, in your telescope, magnify 25x, 31x,
83x, and 111x, respectively. Adding a 2x
Barlow lens will give you
four additional
50x, 62x, 166x,
and 222x.
To find the magnification, or power, of any eyepiece, simply divide the telescope’s
focal length in millimeters (listed in the instruction manual) by the eyepiece’s focal
length (the number printed on the eyepiece’s body). Here’s an example: Celestron’s
SkyProdigy 130 Reflector has a focal length of 650 millimeters. If you choose a 25mm
X-Cel LX eyepiece, the magnification will be 26. If you replace the X-Cel eyepiece with
a 12mm Omni Series eyepiece, the magnification will change to 54. Note that the
type of eyepiece doesn’t affect the magnification. Any two eyepieces with the same
focal length in this telescope will give the same magnifications.
Celestron’s Omni
Barlow lens doubles
the magnification of
any eyepiece. Celestron
Understanding binoculars
inoculars are versatile instruments
with many benefits. They have a wide
field of view and what you see through
them is right-side up, making objects easy
to find. They require no expertise to set up
— just sling them around your neck and
you’re ready to go.
That portability also makes binoculars
ideal for nights when you might not have
the time to set up a telescope. And for most
people, observing with two eyes rather than
one is more natural and comfortable. Most
binoculars also are relatively inexpensive.
• Binoculars give a right-side-up
• They let you use both eyes to
• The biggest sky objects look best
through binoculars.
Roof prism
What the numbers mean
For stargazing, the size of the front lenses is
the most important thing. Generally, the
larger they are, the brighter the image will
be. You can find the lens size by looking at
the two numbers on every binocular: 7x35
or 10x50, for example. The second of those
numbers refers to the size (in millimeters)
of each front lens. So the front lenses of
7x35s have a diameter of 35mm, and
10x50s have a 50mm diameter. Binoculars
with 50mm lenses gather twice as much
light as 35mm binoculars.
Astronomy binoculars should have
lenses at least 40 millimeters across.
Smaller ones may work in the daytime, but
they won’t gather enough light to give good
views of most night sky objects.
The other number is the binoculars’
magnification. For astronomy, go for binoculars that magnify at least 7 times. The
highest you’ll want for hand-held binoculars is about 10x. If the magnification is
higher than that, you likely won’t be able
to hold them steady enough to get a
sharp image. For those, use a tripod.
Porro prism
Binoculars come in two designs: roof prism
and Porro prism. Astronomy: Roen Kelly
Lenses in high-quality binoculars are
made of barium crown glass (BaK-4)
instead of borosilicate glass (BK7). Also,
look for coated optics — the more lens and
prism surfaces to which special coatings
have been applied, the brighter and higher
contrast the images will be.
Most binoculars have a central focusing
knob that moves both eyepieces at once.
These models also have one eyepiece that
you can focus individually. To operate the
binoculars, first use the central knob to
focus the eyepiece that doesn’t
adjust, and then focus the
other eyepiece. This type of
Details to look for
Binoculars contain prisms that make
the image appear right-side up.
These prisms come in two varieties:
roof and Porro. Roof-prism models
have straight barrels and are more
compact. However, they tend to be
more expensive and produce dimmer images, making them less
desirable for astronomy. Porroprism binoculars have a zigzag
shape and usually are bigger and
heavier than roof-prism models.
Skymaster Pro 15x70
binoculars offer premium
optics, high magnification,
and collect a lot of star light.
Cometron 7x50
binoculars offer a
wide field of view
perfect for viewing
the Moon, large
nebulae, and panning
the Milky Way. Celestron
Wide-field views of many astronomical sights
are best seen through binoculars. One favorite
among observers is comets. Martin Moline
focusing proves to be more convenient,
particularly if you pass the binoculars from
person to person. On other binoculars, the
eyepieces focus individually. These models
tend to be more rugged and better sealed
against moisture.
What you’ll see
Binoculars will show the Moon in crisp
detail. Watch shadows creep across lunar
features as the Moon’s phase changes. Follow the stages of a lunar eclipse as Earth’s
shadow covers the Moon. And view a crescent Moon silhouetted against stars low in
the western evening sky.
Farther afield, binoculars let you track
Jupiter’s four big moons. In addition,
they’ll help you pick out Mercury
low in the twilight sky and spot
objects too faint to see easily,
such as the outer gas-giant planets, Uranus and Neptune, as well
as the brighter asteroids.
The advantages of binoculars perhaps show up best when viewing a bright
comet. Binoculars magnify enough to show
detail and have a wide enough field of view
that you can see the comet’s head and most
or all of its tail at once.
Sponsored by Celestron
Become an observer in 10 simple steps
Astronomy remains exciting because something’s always
making news. When you’re an amateur astronomer, not only can
you read about what’s going on, but you can also participate. In
essence, the sky is calling. But how do you start observing the
sky? What do you need to know?
Earth’s axis
of rotation
North Pole
Sketching objects you view through
your scope will make you a better
observer. This drawing shows Jupiter
with two of its moons and their
shadows on the planet. Michael E. Bakich
Learn the sky in a
general sense
Ecliptic (path of the Sun)
Amateur astronomers
should know the basics of
Earth’s rotation and orbit.
Astronomy: Roen Kelly
Constellations change from season to
season. Orion the Hunter (right) is a
winter star pattern. His belt points
down to Sirius, the night sky’s
brightest star. Bill and Sally Fletcher
You’ve made a good start toward becoming
an observer. But there’s a lot more out there
than this booklet, your favorite astronomy
magazine, and the websites of Astronomy
magazine ( and
Celestron (
Your public library and bookshops offer
many other star charts, observing guides,
and texts on all facets of our wonderful
hobby. Except for where you’ll find the
planets on certain dates, such materials
won’t go out of date quickly. Local astronomy clubs can be great resources, too. Make
friends and you’ll quickly learn many tips.
An astronomy shop might let you look through
the telescope you’re thinking of buying. Celestron
Immerse yourself in
the subject
star party hosted by an astronomy club.
Take your time and ask lots of questions.
Amateur astronomers love showing off
their equipment to beginners.
your observing
site carefully
4 Pick
If you’ll be content with the Moon, planets,
and double stars, pretty much any location
will do. To see faint, diffuse objects like
nebulae and galaxies, however, you’ll need
to travel to a dark site.
Some things to consider are how lightpolluted the location is, the driving distance, how portable your telescope is, safety
(will you get cellphone service?), and
weather factors. The last point includes
how generally clear the sky is and how
steady the air is.
6 Comfort is everything
Comfort means a lot more than just
staying warm during the winter. Many
observers use various gyrations while looking through an eyepiece. The one an
observer called the “monkey squat” is
pretty hard on the back and requires keeping several muscles tense to keep your eye
at the eyepiece.
So, sit. When you are seated comfortably
at the eyepiece, you’ll spend more time
observing (and see a great deal more) than
while standing.
Keep a log
You will want to remember what you’ve
seen. A simple log contains the date and
time of your observation, what object(s)
you looked at, and a brief description, like,
“Saw spiral arms!” or “Really blue, but no
details visible.”
More-detailed logs might contain information about the telescope you used, what
eyepiece(s) and magnification(s), and sky
conditions (percent of cloud cover, amount
of light pollution, steadiness of stars, etc.).
9 Become a social astronomer
Visit a planetarium and take in a program. Attend a star party in your area.
Observe with others. Get on the Internet
and chat in one of’s or’s forum areas.
Without question, the best step you can
take is to join a local astronomy club.
Attend its meetings and observing sessions.
This will place you with a group of likeminded people who can either answer your
questions or help you figure out where to
get them answered.
Most astronomy clubs have members
who look for opportunities to share information about the hobby we all love. Get
Light pollution ruins observing sites. To see
faint objects, you’ll need to get out of the city.
Celestron’s NexImage 5 Solar System Imager
lets you capture live video through your
telescope, view it on your screen, and create
high-quality images. Celestron
involved, volunteer to help at events, and
before too long you’ll be the one answering
the questions.
10 Observe it all!
I’ve heard it a million times. “I’m a
planetary observer,” or “I only observe galaxies.” Really? Are these amateur astronomers in fact saying they’d pass up watching
a total lunar eclipse, a bright comet, or a
rich meteor shower?
While your telescope may be best suited
for a particular type of object, you can view
anything through any scope. So why not try
viewing them all?
The Moon has hundreds of targets on its
ever-changing face, and even a small scope
will show most of them. The planets spend
lots of time in the early evening sky, which
makes viewing them convenient. A short
drive each month during the dark of the
Moon may yield dozens of galaxies. While
you take them all in, you’ll surely marvel at
the magnificent universe above and the
richness of the hobby you have chosen.
A star party is a wonderful way
to view through many different
scopes, check out new accessories,
and meet like-minded individuals.
Note that in this picture all the
participants are using red lights.
is rewarding
but time-consuming
7 Photography
Try equipment before
you buy
Some astronomy shops — especially the
ones in major cities — occasionally will set
up equipment for potential customers to
use. At those times, staff will be on hand to
explain how everything operates.
Another way to test-drive a scope is to
attend an observing session or a regional
Try your hand at sketching
If you want to move past simple visual
observing but aren’t ready to commit to
capturing objects with a camera, do some
sketching. Drawing what you see through
the eyepiece lets you record your observations. Sketching is also fun, and you’ll
become a better observer as your ability to
pick out faint details in objects improves.
You won’t need much in the way of supplies. A sketchpad, a #2 pencil, a good
eraser, and a red flashlight will be enough
to get you started. You might also want to
add a drafting compass because most of
what you’ll be sketching is round and any
non-circular objects will lie in the circular
field of view of your telescope’s eyepiece.
South Pole
Michael E. Bakich
It’s good to know some basics: Earth spins
once a day and orbits the Sun once each
year. The first motion causes sky objects to
move from east to west, and the second
causes different constellations to appear in
each season’s sky.
Next, imagine the sky as a sphere with
north and south poles and an equator.
Read up on Moon phases. The Moon
first becomes visible as a thin crescent low
in the western evening sky. Each night
thereafter, it appears to grow and move
eastward until Full Moon, after which its lit
part shrinks to invisibility (New Moon).
When you again spot the thin crescent low
in the west, roughly 30 days have passed.
You’ll want to know the Moon’s phase
because its light can prevent you from seeing faint objects.
Finally, become familiar with bright seasonal constellations. Start with just a couple
per season: Taurus the Bull and Orion the
Hunter in winter; Scorpius the Scorpion
and Cygnus the Swan in summer; and so
on. Don’t worry about the faint ones. If you
haven’t heard of them — for example, Lacerta and Serpens — there’s probably a good
reason why.
then you process that image with the right
Lots of resources exist to help you learn
the art of astrophotography. Read all you
can, take lots of images, and eventually
you’ll proudly show off your results to family and friends.
Phil Jones
Here’s the good news: You can take pictures
of astronomical objects. Here’s the other
side: Astroimaging takes practice, and there
is a learning curve. The higher the quality
of the final image, the steeper the curve.
Remember that producing a high-quality
picture involves two stages. First you
acquire the data through your camera, and
Sponsored by Celestron
Start exploring the sky
with you
Congratulations on your telescope purchase.
Here are some suggested objects to observe.
One of the most pleasurable observing
experiences you can have under the summer or winter sky is simply scanning the
Milky Way through your telescope. It’s so
simple — just insert an eyepiece that gives a
wide field of view (one with a large number
on it), shut down your laptop, ignore your
observing guides, turn off your go-to drive,
and move your scope to and fro by hand.
Observe the Sun
You can double your
observing fun with
a safe solar filter.
A filter that fits
over the front of
your telescope is
the only kind to use.
Never look directly at
the Sun with your eye Observing the Sun
will allow you to use
or through any unfilyour scope during
tered telescope.
the daytime. Be sure
You can start your
to use a safe solar
solar observing by
filter. Alan Friedman
counting or sketching
sunspots. It’s fun, its’ easy, and sunspot
counts let you know just how active the Sun
is. People have been recording sunspot
numbers daily since 1749.
Jamie Cooper
Observe the Moon
Observe Jupiter
Next to the Sun and Moon, Jupiter has the
most detail. The planet’s four largest moons
look like bright stars generally in a line on
either side of Jupiter.
Along with the moons, two dark stripes
— the North and South Equatorial Belts
— are easy to see. If the atmosphere above
your site is steady, use higher magnifications (eyepieces with lower numbers
printed on them). You’ll see that Jupiter
looks a bit oblong because it spins fast and
is not a solid planet.
double stars
Although stars look
like a single point of
light to the naked
eye, your telescope
will split many of
Albireo, a star in the
constellation Cygnus
them into pairs.
the Swan, is just one
Observing double
of hundreds of
stars is easy, it
colorful double stars
doesn’t take a comyou can see through
plicated setup, you
your scope. Dietmar Hager
can observe from a
city, and targets exist for every size telescope. Plus, you’ll see lots of colors.
In addition to how bright each component of the double star is, one number will
let you know if your telescope can split it.
It’s the pair’s “separation” — the visual distance between the two stars. It’s given in
Observe Messier’s list
Charles Messier (1730–1817) was a French
comet-hunter. During his searches, he
encountered dozens of objects that looked
like comets but didn’t move against the
starry background.
In 1758, he discovered what he thought
was a comet. This object became the first
entry — M1 — in his famous catalog of
comet “imposters.” Working your way
through Messier’s list will introduce you to
some of the best and brightest star clusters,
nebulae, and galaxies.
The size of your telescope will influence which double stars you observe.
Bigger scopes can resolve smaller
separations. Use this table as a general rule to determine the minimum
double star separation your telescope
will split. Weather conditions may
affect your success.
you’ll split
lets you:
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The Moon has a face that’s always changing. But Full Moon is not the best time to
view it. That’s when there are few shadows,
so you’ll see little detail.
The best evening
views are between
New Moon and 2
days after First
Quarter. In the
morning before sunrise, view from
about 2 days before
Last Quarter to just
before New Moon.
The Moon offers a
Shadows are longer
changing face, superb
at these times, and
shadow details, and
lunar features really
thousands of
fascinating features.
stand out.
Mainly look along
the line dividing the
light and dark portions, called the terminator. There,
you’ll see mountaintops high enough to
catch sunlight while
Enjoy the Milky Way in the summer or winter, when it’s highest in the sky.
dark lower terrain
surrounds them. On
large crater floors, you can follow “wall
arcseconds, noted by the symbol ". One
shadows” cast by the sides of craters hunarcsecond (1") equals 1/3,600 of 1°. See the
dreds of feet high. All these features change table below for the double star separation
in real time, and the differences you can
your telescope can split.
see in just one night are striking.
Tunç Tezel
Scan the Milky Way
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