Note: The Guide Star Catalog has been constructed to support the
operational need of the Hubble Space Telescope.
It contains over 25 million positions for about 19 million
objects, of which more than 15 million are classified as stars.
The version 1.2 is a new astrometric reduction which results in
absolute position errors about 0.3-0.4 arcsec.
(see GSC pages at URL http://www-gsss.stsci.edu/gsc/gsc.html)
Note: Detailed introduction can be found in intro.tex (see also http://aries.usno.navy.mil/ad/ac.html) Direct links to Hipparcos and Tycho observations are provided from the relevant columns.
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