Email: nexusmail at this Web site address
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.
Choose the version of the database that best serves your needs:
About the HYG Database
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 astronomers:
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.*
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 magnitude.
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:
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.
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.