The Astronomy Nexus
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The HYG Database
Subm itted by David on Sat, 2006-03-18 04:26
About This Site
About Me
My Other Interests
Update (19 Sept 2011): The current version of the database is now hosted at Github.
The HYG database (v2.0) is a compilation of interesting (to me, anyway) stellar data
from a variety of catalogs. It is useful for background information on all sorts of data:
star names, positions, brightnesses, distances, and spectrum information.
Stellar Cartography
Choose the version of the database that best serves your needs:
Distant Worlds Star Mapper
HYG Database
Encyclopedia of Suns
3D Universe
The Armchair Astrometrist
HYG 2.0: Database containing all stars in Hipparcos, or closer than 50 parsecs.
This also includes velocity information, which was missing from the previous
database. (almost 120,000 stars, 9 MB)
HYG v1.0 (to 7.5): Database containing all stars brighter than magnitude +7.5, or
closer than 50 parsecs. This is the same as the "Version 1.0" database that has
been on this site before. (31858 stars)
Observing Guides
HYG v1.1 to 8.0: Database containing all stars brighter than magnitude +8.0, or
closer than 50 parsecs. (46786 stars)
Virtual Messier
sci.astro.amateur FAQ
Variable Stars
HYG v1.1 to 8.5: Database containing all stars brighter than magnitude +8.5, or
closer than 50 parsecs. (66392 stars)
Full v 1.1 database: Database containing all stars brighter than magnitude +9.0, or
closer than 50 parsecs.(87476 stars)
About the HYG Database
Personal Experiences
Clubs and Organizations
The Nebraska Star Party
Southern Peru, 1994
Other things I've written
The database is a subset of the data in three major catalogs: the Hipparcos
Catalog,the Yale Bright Star Catalog (5th Edition), and the Gliese Catalog of Nearby
Stars (3rd Edition). Each of these catalogs contains information useful to amateur
The Hipparcos catalog is the largest collection of high-accuracy stellar positional
data, particularly parallaxes, which makes it useful as a starting point for stellar
distance data.
Other interests
3D graphics gallery
Technical illustration
The Yale Bright Star Catalog contains basic data on essentially all naked-eye
stars, including much information (such as the traditional Bayer Greek letters and
Flamsteed numbers) missing from many other catalogs
The Gliese catalog is the most comprehensive catalog of nearby stars (those
within 75 light years of the Sun). It contains many fainter stars not found in
The name of the database comes from the three catalogs comprising its data:
Hipparcos, Yale, and Gliese.
All told, this database contains ALL stars that are either brighter than a certain
magnitude cutoff (magnitude +7.5 to +9.0) or within 50 parsecs (about 160 light
years) from the Sun. The current version, v. 2.0, has no magnitude cutoff: any star in
Hipparcos, Yale, or Gliese is represented.
The database is a comma separated values (CSV) file that can be imported into
most database and spreadsheet programs. On this web site it is stored as a Zip file
or a GZ file, which most popular unzippers can open.
Be aware that many spreadsheet programs (Excel, for example) have a cutoff of 64K
(65,536) lines of input from a CSV or similar file. If you plan to use a spreadsheet
program to play with the data, you may have an easier time with the two smaller
databases (7.5 and 8.0 magnitude cutoffs).
Fields in the Database
Fields labeled with "*" exist only in version 2.0. Also, since I used a larger set of data
for this version, the StarID differs from versions 1.*
1. StarID: The database primary key from a larger "master database" of stars.
2. HD: The star's ID in the Henry Draper catalog, if known.
3. HR: The star's ID in the Harvard Revised catalog, which is the same as its
number in the Yale Bright Star Catalog.
4. Gliese: The star's ID in the third edition of the Gliese Catalog of Nearby Stars.
5. BayerFlamsteed: The Bayer / Flamsteed
designation, from the Fifth Edition of the Yale Bright Star Catalog. This is a
combination of the two designations. The Flamsteed number, if present, is
given first; then a three-letter abbreviation for the Bayer Greek letter; the Bayer
superscript number, if present; and finally, the three-letter constellation
abbreviation. Thus Alpha Andromedae has the field value "21Alp And", and
Kappa1 Sculptoris (no Flamsteed number) has "Kap1Scl".
6. RA, Dec: The star's right ascension and declination, for epoch 2000.0. Stars
present only in the Gliese Catalog, which uses 1950.0 coordinates, have had
these coordinates precessed to 2000.
7. ProperName: A common name for the star, such as "Barnard's Star" or
"Sirius". I have taken these names primarily from the Hipparcos project's web
site, which lists representative names for the 150 brightest stars and many of
the 150 closest stars. I have added a few names to this list. Most of the
additions are designations from catalogs mostly now forgotten (e.g., Lalande,
Groombridge, and Gould ["G."]) except for certain nearby stars which are still
best known by these designations.
8. Distance: The star's distance in parsecs, the most common unit in
astrometry. To convert parsecs to light years, multiply by 3.262. A value of
10000000 indicates missing or dubious (e.g., negative) parallax data in
9. Mag: The star's apparent visual magnitude.
10. AbsMag: The star's absolute visual magnitude (its apparent magnitude from
a distance of 10 parsecs).
11. Spectrum: The star's spectral type, if known.
12. ColorIndex: The star's color index (blue magnitude - visual magnitude),
where known.
13. * X,Y,Z: The Cartesian coordinates of the star, in a system based on the
equatorial coordinates as seen from Earth. +X is in the direction of the vernal
equinox (at epoch 2000), +Z towards the north celestial pole, and +Y in the
direction of R.A. 6 hours, declination 0 degrees.
14. * VX,VY,VZ: The Cartesian velocity components of the star, in the same
coordinate system described immediately above. They are determined from
the proper motion and the radial velocity (when known). The velocity unit is
parsecs per year; these are small values (around 10-5 to 10 -6 ), but they
enormously simplify calculations using parsecs as base units for celestial
Database Construction
I came up with this database while creating the 3D Universe web site. I needed a
reference that would let me search for groups of stars by magnitude or distance,
while giving me more information than was contained in any one catalog.
I started with the Hipparcos data. The Hipparcos data set represents by far the most
comprehensive collection of stellar distance and brightness data in existence, except
for very low-luminosity stars. Essentially all naked-eye stars (in fact, most stars down
to about apparent magnitude +9 and many others down to about +11) are
represented in the Hipparcos catalog.
In older versions of the dataset, I first prepared a subset of the Hipparcos data. I did
this for boring technical reasons that no longer apply, so version 2.0 uses the entire
Hipparcos catalog.
I next consulted the Gliese catalog to fill in gaps in the Hipparcos catalog, and to add
various Gliese data to the catalog. In particular, the Gliese catalog ID is a common
reference for nearby stars, and the Gliese catalog contains radial velocity data, which
Hipparcos lacks. Additionally, though Hipparcos distances are generally superior to
Gliese data, the Hipparcos catalog missed many nearby stars that were below its
magnitude cutoff.
To cross-reference stars, I used the Henry Draper catalog number, whenever
present, to add Gliese data to the Hipparcos catalog. Many of the faintest stars
lacked this catalog number, so I compared the positions and brightnesses of Gliese
stars to those in Hipparcos, and if they matched to within a certain tolerance, I
assigned the appropriate Gliese data to the Hipparcos star. Stars that failed both
references were then added to the end of the Hipparcos list.
I also converted Hipparcos apparent magnitudes to Gliese values for all components
of known multiple stars in the latter catalog. Again, the Hipparcos magnitude
measurements are often superior, but the Hipparcos catalog treats multiple stars
inconsistently. In particular, it breaks some out as separate stars (e.g., Alpha
Centauri) but merges others (such as Capella, 70 Ophiuchi, and many others). By
contrast the Gliese catalog breaks all known multiple stars, excluding those too
close to be separated optically, into their components, and gives each one a
I then calculated absolute magnitudes for all stars, added those to the database, and
added about 250 proper names. Then, again using Henry Draper as a cross
reference, I added data from the Yale Bright Star Catalog: HR numbers, radial
velocities (if not already added from Gliese), and the Bayer and Flamsteed
designations. Finally, I added a number of radial velocities from the Wilson Evans
Batten catalogue to stars that didn't already have that information.
These steps resulted in the full database. To make the various subsets, I took the
resulting database and extracted subsets of the data.
Database Quality Issues
With over 100,000 stars to worry about, I generally couldn't go in and edit suspect
records by hand. Consequently, there are some issues that serious users may want
to be aware of:
The spectral types, in general, come from the Hipparcos catalog. A few stars -those found only in Gliese, have a spectral type from that catalog. The spectral
types from Hipparcos have not been closely vetted and I have already found some
probable errors. For example, the spectral type of 36 Ophiuchi B (a double star that
was merged in Hipparcos) is given as K2 III (giant), when its luminosity clearly
indicates K2 V (main sequence). Also, the star HIP 84720 (Gliese 666 A) is listed
as M0 V, whereas its luminosity and color index are more consistent with a late Gtype star (about G8 V). M0 V appears to be the spectral type of Gliese 666 B, a
companion to this star. Use the spectral types with caution.
There may be errors in the Henry Draper numbers in one or more catalogs,
leading to false cross-references.
There may be errors in the matching of Gliese stars to Hipparcos stars by position
and magnitude. In general, this is likely to be an issue only for multiple stars with
highly uncertain magnitudes in both catalogs, as the position constraints were
fairly severe (stars had to have positions matching to +/- 0.15 degrees, less than
the radius of the full Moon). I have not seen any apparent errors on scanning the
database thus far, but this is one area that could be a problem.
Radial velocity information can be quite uncertain. Uncertainties of a few
km/second are not unusual. There are 3 primary sources: the values in the Gliese
catalog, the values in the Yale catalog, and the Wilson Evans Batten catalog
mentioned earlier, in that order. I do not yet have a detailed breakdown of the
uncertainties in these sources.
In short, though I have done what I can, I can't warrant the database to be error-proof.
If you need to launch probes to all the stars in the database, you might want to give it
a more thorough going-over before doing so :-)
More techie stuff
I have created a short Perl script that will read the database as is (no need to import
it into another program), run a SQL query on it, and then save the query results to an
HTML page for viewing. It uses Microsoft's Open Database Connectivity (ODBC)
drivers and so, right now, only works on Windows platforms. The script is very much
beta; it also requires the Perl executable, a basic knowledge of SQL, and enough
general geekiness to edit a Perl script without killing it. I will E-mail it to anyone who
is interested, and will post a copy of it here if interest is high enough.
If none of that makes any sense, just pop the CSV file into your favorite database or
spreadsheet program, and ignore the previous paragraph.
Other Issues
The data in this database are subject to change. I may add or delete stuff as I feel
like. If there are any really large changes, I will post copies to this site.
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