unique GSCII Objects
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
of the near infrared plates and the POSS-I plates in the north
is still ongoing.
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
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
catalog. Please read the release
notes for additional details on the GSC2.2, and check
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
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 use policy • data
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