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NOTE: Most of the High Level Science Products are unavailable while unscheduled maintenance is being performed. They will be incrementally restored over the course of this week. We apologize for any inconvenience.

Getting Started


The Catalogs and Surveys Group (CASG) of the Space Telescope Science Institute (STScI) digitized the photographic Sky survey plates from the Palomar and UK Schmidt telescopes to produce both the Digitized Sky Survey (DSS), and the Guide Star Catalogs (GSC). The catalogs support ground and space-based telescope operations and provide a valuable scientific resource to the astronomical community.

GSC-I was constructed primarily to support the operational requirements of the Hubble Space Telescope for off-axis guide stars. Production scanning began in 1985 and continued through 1988. Catalog construction was performed in parallel with the scanning. It proceeded in stages as production software became available, first for sky-following and object inventory, and later for classification plus photometric and astrometric calibrations. GSC-I contains approximately 19 million stars and other objects in the sixth to fifteenth magnitude range.

GSC-II will obtain proper motion and color information in addition to accurate coordinates, magnitudes and classifications for all objects down to at least 18th magnitude. The all-sky, magnitude-limited Telescope Operations version, GSC2.2, contains positions, classifications, and magnitudes for nearly a half billion objects, and is now available.

See the CASG home page for the latest news and developments. See also the CASB pages on: