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.

I/252/out Post annotation

The USNO-A2.0 Catalogue (Monet+ 1998) ReadMe+ftp metaI/252/out The Full Catalogue (526280881 rows) (Note)

Full	_RAJ2000 "h:m:s"	_DEJ2000 "d:m:s"	_RAB1950 "h:m:s"	_DEB1950 "d:m:s"	_Glon deg	_Glat deg	USNO-A2.0	RAJ2000 deg	DEJ2000 deg	ACTflag	Mflag	Bmag mag	Rmag mag	Epoch yr
1	03 46 19.57272	+23 56 53.9700	03 43 21.25439	+23 47 36.7562	166.56993679	-23.74922046	1125-01259575	056.581553	+23.948325	A		99.9	4.2	0.000