Guide Star Catalog II

STScI ACDSD MASTCASB GSC

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Last Updated Jan 2001

Copyright 2001 The Association of Universities for Research in Astronomy, Inc. All Rights Reserved.

998,402,801 unique GSCII Objects
and counting!


The GSC II is an all-sky 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 (DSS). Positions, magnitudes, and classifications are produced for all objects on each plate. The objects are then loaded into the COMPASS database, where multiple observations of the same object are matched and assigned a unique name based on the HTM sky tesselation that has become a community standard. This provides the multi-wavelength, multi-epoch data necessary to produce colors and proper motions.

Construction of the complete GSC-II is still in progress. More than 998 million unique objects have been loaded into the COMPASS database thus far, based on plate-limited image processing and calibrations for all sky survey plates in two bandpasses (J and F) in both hemispheres. Processing of the near infrared plates and the POSS-I plates in the north is still ongoing.

The GSC2.2 is an allsky, magnitude-selected subset of this data that has been extracted to support telescope operations at the GEMINI and VLT telescopes. As of July 16, 2001, this Telescope Operations version 2.2.01 contains positions, classifications, and magnitudes for 455,851,237 objects, and is now available to the community via the WWW. The magnitude limits (18.5 in photographic F or 19.5 in photographic J) were implemented to ensure the photometric quality of the released data. Since bright objects are extremely overexposed on the Schmidt plates, we have replaced these bright objects with those from the Tycho-2 catalog. Please read the release notes for additional details on the GSC2.2, and check the catalog properties page to see how it updates and extends its predecessor, the GSC I.

The final version (GSC 2.3), expected to be released in 2003, will also contain proper motions.

The catalog will be used for operational support of HST, the GEMINI telescopes, ESO's Very Large Telescope (VLT) as well as future space missions such as the Next Generation Space Telescope (NGST).

Please note that GSC 2.2.01 is 40GB in size and that we do not have the resources to support downloads or make copies of the entire catalog for individual researchers or institutions at this time - only participating institutions. We are looking at options and costs for a mass distribution of GSC 2.3 on some media. The major data centers and observatories which contributed to the production of this catalog are also providing on-line access to the world-wide community.


Please read the fine print:

data copyrights data use policy data acknowledgements


The Guide Star Catalogue II is being constructed by the Catalogs and Surveys Branch of the Space Telescope Science Institute and the Osservatorio Astronomico di Torino in collaboration withthe Astrophysics division of ESA, the GEMINI project and the ST-ECF .