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.

Full	_r arcsec	_RAJ2000 "h:m:s"	_DEJ2000 "d:m:s"	USNO-A2.0	RAJ2000 deg	DEJ2000 deg	ACTflag	Mflag	Bmag mag	Rmag mag	Epoch yr
1	1.781	23 28 33.07008	-22 30 29.3904	0600-44583421	352.137792	-22.508164			13.1	11.3	1982.065
2	9.328	23 28 32.74152	-22 30 23.3532	0600-44583374	352.136423	-22.506487			16.6	15.5	1982.065

%0a%0a%3cP%3e%0a%3cFONT%20SIZE=%27-1%27%3e%3cEM%3e%3cFONT%20COLOR=%27#0000FF%27>%3cB%3eNote:%20The%20%3cB%3eGuide%20Star%20Catalog%20has%20been%20constructed%20to%20support%20the%20%0aoperational%20need%20of%20the%20Hubble%20Space%20Telescope.%0aIt%20contains%20over%2025%20million%20positions%20for%20about%2019%20million%0aobjects,%20of%20which%20more%20than%2015%20million%20are%20classified%20as%20stars.%0aThe%20version%20%3cB%3e1.2%20is%20a%20new%20astrometric%20reduction%20which%20results%20in%0aabsolute%20position%20errors%20about%200.3-0.4%20arcsec.%0a%28see%20GSC%20pages%20at%20URL%20http://www-gsss.stsci.edu/gsc/gsc.html%29%0a%3cP%3e%0a

Full	_r arcsec	_RAJ2000 "h:m:s"	_DEJ2000 "d:m:s"	GSC	RAJ2000 deg	DEJ2000 deg	PosErr arcsec	Pmag mag	e_ mag	n_	Class	Plate	Epoch yr
1	1.77	23 28 33.0720	-22 30 29.376	0698000167	352.13780	-22.50816	0.3	13.42	0.40	0	3	04LP	1977.553
2	1.84	23 28 33.0648	-22 30 29.376	0698000167	352.13777	-22.50816	0.4	13.84	0.40	0	3	04LU	1980.826

%0a%0a%3cP%3e%0a%3cFONT%20SIZE=%27-1%27%3e%3cEM%3e%3cFONT%20COLOR=%27#0000FF%27>%3cB%3eNote:%20The%20%3cB%3eGSC-ACT%20%3cEM%3e%28or%20%3cB%3eGSC1.3%29%0ais%20a%20recalibration%20of%20the%20%3cB%3e<%25E%20I/220%7cGSC1.1>,%20the%20catalogue%20constructed%20%0ato%20support%20the%20operational%20need%20of%20the%20Hubble%20Space%20Telescope,%0awith%20the%20%3cB%3e<%25E%20I/246%7cACT>,%20the%20combination%20of%20the%20Astrographic%20Catalogue%0aand%20the%20%3cB%3e%3cEM%3eTycho%20catalogue%20derived%20from%20the%20%3cEM%3e<%25E%20I/239%7cHipparcos>%0amission;%20see%20http://www.projectpluto.com/gsc_act.htm%20for%20more%20details%0aabout%20this%20recalibration.%0a%3cP%3e%0a

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