Note: Errors found in the Hipparcos catalogue are reported in the file errata.htx
Note: Note that the errors on the proper motions are large (∼50mas/yr), and therefore the positions computed at an epoch different from 1991.25 have a large (∼0.4") uncertainty. The Tycho Epoch Photometry data can be accessed from the morePhoto column (includes VT, BT and Hp photometric data for Hipparcos stars [filter responses]
Note: Direct links to the Hipparcos and Tycho data (catalog I/239) are provided when relevant
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: The construction of the GSC-II is still in progress: this version has no proper motions, and the magnitude limits are 18.5 in F (red) and 19.5 in J (blue). The data are copyrighted, check the data use Policy.
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.
Note: This version of the GSC-II has no proper motions, but the limits on brightness which existed on GSC2.2 (F<18.5, Bj<19.5) were removed.
