Note: USNO-A2.0 contains 526,280,881 sources, and is based on a re-reduction of the Precision Measuring Machine (PMM) scans from POSS-I O and E plates (>=-18°) and SRC-J and ESO-R plates (<=-20°). USNO-A2.0 was created by Dave Monet () and collaborators at Flagstaff Station, U.S. Naval Observatory. The major difference between USNO-A2.0 and its previous version USNO-A1.0 is that A1.0 used the Guide Star Catalog as its reference frame whereas A2.0 uses the ICRF as realized by the USNO ACT catalog (Urban et al. 1997). The VizieR search engine uses an on-line compressed version (3.6Gbytes) which was generated at CDS.
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 USNO-B Catalog presents positions, proper motions, magnitudes un blue, red and infrared, as well as star/galaxy estimators for 1,045,175,762 objects derived from 3,648,832,040 separate observations. The data were taken from scans of 7,435 Schmidt plates taken from various sky surveys during the last 50 years. USNO-B1.0 catalog was created by Dave Monet and collaborators at http://www.nofs.navy.mil/data/fchpix/ Note that the star/galaxy estimators may be mixed up in dense regions.
