HST Guide Star Catalog v1.1:
Catalog Help
The GSC was constructed from 1477 Schmidt plates covering the standard
survey grids plus 39 supplemental plates. The GSC as distributed on the
cd-roms contains 25,126,027 entries for 18,819,291 objects with
magnitudes between 8.5 and 15. Of these 15,169,873 are stars and
3,649,418 are not. The GSC as contained in the LEDAS database has
been compressed to only have one entry per object. This compression
process finds 18,818,613 objects, 678 objects fewer than advertised.
Each entry contains a position, a Quasi-V magnitude (`QV mag`) and a
Quasi-B magnitude (`QB mag`). The former comes mostly from the northern
Palomar survey, and the latter from the UK SERC Schmidt survey. Near
equatorial regions, where the surveys overlap, both magnitudes are
available. But for the majority of cases only one or the other will be
given. A code (`CV` and `CB`) gives further information on the emulsion
and filter used.
The default cone search radius is 1 arc minute. Be careful in selecting
larger values for the cone search radius: for example, setting it to be
30 arcminutes will typically result in a sample that contains hundreds,
if not thousands, of stars. We recommend that cone search radii of more
than 30 arcminutes not be used.
We recommend that cone searches should not exceed a radius of 30 arc min,
since, as you will quickly discover, a radius of 30 arc mins usually
contains hundreds if not thousands of stars. To `cover' a larger area,
then, you should do a mosaic of 30 arc minute searches with offset
co-ordinates. Notice that the default cone search radius is 1 arc minute.
GSC number
The catalog number of the star.
RA1950/2000
The Right Ascension of the star at the requested epoch.
Dec1950/2000
The Declination of the star at the requested epoch.
Mag
Since the GSC is drawn from two overlapping surveys, the quoted
magnitude may be either a Quasi-V magnitude (`QV mag`) or a
Quasi-B magnitude (`QB mag`). The former comes mostly from the northern
Palomar survey, and the latter from the southern UK SERC Schmidt survey.
Class
The classification flag uses the following codes:
------------------------------------------------------------------------
Code Meaning
---- -------
1 Star
2 Galaxy
3 Non-Star
5 Artifact
------------------------------------------------------------------------
Radius
Distance from search centre in arcsec.
The full details of the GSC catalog are contained in the Space Telescope
Preprint No. 363.
