Hubble Space Telescope
Guide Star Catalog
The original version of this catalogue was created to support the
identification and use of Guide Stars for the pointing of the HST. It is
based on the Palomar Quick-V survey in the northern hemisphere and the
SERC-J survey in the south. This catalogue contains objects in the magnitude
range 7-16 and the classification was biased to prevent the use of a
non-stellar object as a guide star. The photometry is based on a
photoelectric sequence (9-15th mag) near the center of each Schmidt plate.
Only stellar photometry was performed so magnitudes of galaxies in this
catalog are systematically in error. Astrometry was determined using the
AGK3, SAOC or CPC stars depending on plate declination. Although the
relative astrometry (required for HST) is about 0.3 arcsec, there are
known systematic errors near the plate edges of about 1-2 arcsec.
A revised version of the GSC was created with the cooperation of the
HIPPARCOS/TYCHO consortia. As part of the preparation for this mission,
an input catalogue containing the best available data for all stars to at
least 11th magnitude was created. By merging these data with the GSC, we
were able to add the missing bright star data to provide a complete all-sky
catalogue down to the GSC limiting magnitude. In addition, many of the
false objects due to artifacts around the halos and diffraction spikes of
the bright stars were identified and corrected as well as a number of
reported errors. A number of astrographic plates centered on southern
hemisphere bright stars (m<3) were also processed and added to the catalogue.
This is the version currently used by HST operations and published to the
To enable rapid access of specific stars in the catalog,
numbers each star using its region number (0001-9537) and a four-digit
star number within each region, separated by a decimal point.
sgsc lists GSC stars by
number or sky region.
imgsc lists the ACT stars
within an IRAF or FITS image with a world coordinate system defined in its
header. The catalog can also be
plotted by skymap.
The HST GSC contains nearly 19 million objects brighter than sixteenth
magnitude, of which more than 15 million are classified as stars. They are
organized into 9537 regions on the sky. The parts of the sky covered by
the regions are tabulated in the tables/regions.tbl file which is
found on each CDROM. The sources in each region are
in separate FITS ASCII tables files which contain source number within the
region, right ascension and declination in degrees to five decimal places,
position error in arcseconds, magnitude to .01 magnitude, error to .01
magnitude, class, bandpass, and a flag to tell how many entries there are
for that object.
GSC Classification Codes
3 Non-star (can be galaxies, blended objects, defects, etc)
The multiple flag is used to flag the same object appearing on more than one
GSC Bandpass Codes
0 : J photographic IIIaJ + GG495
1 : V photographic IIaD + W12
2 : FGS
3 : B photoelectric
4 : V photoelectric
5 : R photographic IIIaF + RG630
6 : V495 photographic IIaD + GG495
7 : O photographic 103a0 + no filter
The purpose of the GSC-ACT project is to recalibrate the Hubble Guide Star
Catalog (GSC), version 1.1, using the ACT (Astrographic Catalog/Tycho) data
from the US Naval Observatory. The recalibrated catalog might be
available on CDROM,
and a GSCACT option which does the recalibration on the fly may be added to
- The Guide Star Catalog I. Astronomical Foundations and Image Processing
- B.Lasker, C.Sturch, B.McLean, J.Russell, H.Jenkner, M.Shara
- The Astronomical Journal, 1990, Volume 99, pg.2019.
- The Guide Star Catalog II. Photometric and Astrometric Models and Solutions.
- J.Russell, B.Lasker, B.McLean, C.Sturch, H.Jenkner
- The Astronomical Journal, 1990, Volume 99, pg.2059.
- The Guide Star Catalog III. Production, Database Organization, and Population Statistics.
- H.Jenkner, B.Lasker, C.Sturch, B.McLean, M.Shara, J.Russell
- The Astronomical Journal, 1990, Volume 99, pg.2081.
- The Guide Star Catalog IV. User Interfaces, Utilities, and Astronomical
Applications. IN PREPARATION
- The Tycho Input Catalogue - Cross-matching the Guide Star Catalog with
the Hipparcos INCA Data Base.
- D.Egret, P.Didelon, B.McLean, J.Russell, C.Turon
- Astronomy and Astrophysics, Vol. 258, no. 1, p. 217-222.
[GSC at HST]