Note: USNO-A1.0 contains 488,006,860 sources, and was compiled from the blue/red overlaps of the detection lists generated from scans of POSS-I O and E plates (>=-30°) and SRC-J and ESO-R plates (<=-35°). USNO-A1.0 was created by Dave Monet () and collaborators at Flagstaff Station, U.S. Naval Observatory; it is superseded by the new PMM-USNO-A2.0 version. The VizieR search engine uses an on-line compressed version (3.4Gbytes) which was generated at CDS.
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 current version includes only the North (POSS-I plates)
