The Guide Star Catalogs were created by the staff of the Catalogs and Surveys Branch of the Space Telescope Science Institute.

The Guide Star Catalog I (GSC I) is an all-sky optical catalog of positions and magnitudes of approximately 19 million stars and other objects in the 6th to 15th magnitude range. GSC I catalog is used for the control and target acquistion of the Hubble Space Telesope. The Guide Star Catalog II (GSC II) is an all-sky optical catalog based on 1" resolution scans of the photographic Sky Survey plates, at two epochs and three bandpasses, from the Palomar and UK Schmidt telescopes. The GSC II is an all-sky catalog of approximately 2 billion stars and galaxies containing positions, magnitudes,colors and proper motions complete to a minimum of V =18.

The Guide Star Photometric Catalog (GSPC-I) is an all-sky set of photoelectrically determined BV sequences in the magnitude range from 9 to 15, generally near the centers of the fields of the GSC-I plates. GSPC II is an all-sky catalog of secondary "standard-stars" that were used to perform the photometric calibration of the GSC-II. GSPC II is generally an extension of GSPC I sequences to V=19 in (B), V and R passbands based on CCD photometry. Its purpose is calibration of the GSC-II. New northern sequences are being added to support the POSS-II.

GSC 2.3 now available!.