The Guide Star Catalog (GSC), also known as the ''Hubble Space Telescope, Guide Catalog'' (''HSTGC''), is a

star catalog A star catalogue is an astronomical catalogue that lists stars. In astronomy, many stars are referred to simply by catalogue numbers. There are a great many different star catalogues which have been produced for different purposes over the years, ...

compiled to support the

Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most vers ...

with targeting off-axis stars. GSC-I contained approximately 20,000,000 stars with apparent magnitudes of 6 to 15. GSC-II contains 945,592,683 stars out to magnitude 21. As far as possible, binary stars and non-stellar objects have been excluded or flagged as not meeting the requirements of Fine Guidance Sensors. This is the first full sky star catalog created specifically for navigation in outer space.

History

Version 1.0

The first version of this catalog was published in 1989. The first catalog was created by digitizing photographic plates produced by the Palomar Schmidt Quick-V survey for the northern hemisphere and the UK Schmidt SERC-J survey for the southern hemisphere. This catalog 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. Stellar photometry was performed in a manner that would systematically reject galaxies. Astrometry was determined using the

AGK3 The ''Astronomische Gesellschaft Katalog'' (AGK) is an astrometric star catalogue. Compilation for the first version, AGK1, was started in 1861 by Friedrich Argelander and published between 1890 and 1954, listing 200 000 stars down to ninth m ...

, SAOC or CPC catalog stars depending on plate declination. Although the relative astrometry (required for HST) is about 0.3 arc seconds, there are known systematic errors near the plate edges of 1 to 2 arc seconds.

Version 1.1

The first revision of the catalog was published in 1992. The Tycho Input Catalog was created by the Hipparcos/Tycho international consortia in preparation for the Hipparcos satellite mission. They produced a catalog containing the best available data for all stars to magnitude 11. Adding the bright star data from this catalog to the GSC produced a complete all-sky catalog 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 (of magnitude less than 3) were also processed and added to the catalog. This was the version used by HST operations prior to cycle 15.

Version 1.2

Version 1.2 was published in 2001. It was produced in collaboration with the

Astronomisches Rechen-Institut The Astronomical Calculation Institute (german: Astronomisches Rechen-Institut; ARI) is a research institute in Heidelberg, Germany, dating from the 1700s. Beginning in 2005, the ARI became part of the Center for Astronomy at Heidelberg Univers ...

Heidelberg Heidelberg (; Palatine German language, Palatine German: ''Heidlberg'') is a city in the States of Germany, German state of Baden-Württemberg, situated on the river Neckar in south-west Germany. As of the 2016 census, its population was 159,914 ...

. This version reduces the plate-based position-dependent and magnitude-dependent systematic errors. The PPM and AC reference catalogs were used and absolute position errors have been reduced to between 0.3 and 0.4 arc seconds.

Catalog format

When quoting a catalog entry, the format is ''GSC FFFFF-NNNNN'', or alternately, ''GSCfffff0nnnnn'' (fffff0nnnnn). The F-sequence references a Hubble sky region code.

Guide Star Catalog II

A significant expansion of the catalog, Guide Star Catalog II, was published in 2008. The Guide Star Catalog II (GSC-II) was compiled by the Catalog and Surveys branch of the

Space Telescope Science Institute The Space Telescope Science Institute (STScI) is the science operations center for the Hubble Space Telescope (HST), science operations and mission operations center for the James Webb Space Telescope (JWST), and science operations center for the ...

and the astrometry team of the Astronomical Observatory of Torino (Italy). It has entries for 945,592,683 stars, and has positions, classifications, and magnitudes for 455,851,237 stars. The latest revision of this version (2.3.4) is in active use for accurately positioning the

References

External links

GSC I and GSC II home

{{Hubble Space Telescope Hubble Space Telescope Astronomical catalogues of stars