LEDAS  
BLASTA Leicester Database and Archive Service
 
BLASTA Help
  2MASS
  ACT
  GSC
  GSC-2.2
  GSC-ACT
  SDSS-DR7
  PPM
  SAO
  Tycho-2
  UCAC2
  USNO-A2.0
  USNO-B1.0
Line
Footer
E-mail

HST Guide Star Catalog v1.1:
Catalog Help


Overview

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.


Parameters

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.


Reference

The full details of the GSC catalog are contained in the Space Telescope Preprint No. 363.

 
HOME
SEARCH
SERVICES INFO SOFTWARE ViZieR BLASTA DSS
ARCHIVES ASCA CHANDRA GINGA ROSAT ARNIE