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	0.444	21 04 33.54888	+19 48 02.8620	1050-19140050	316.139787	+19.800795			14.9	14.5	1953.748
2	5.795	21 04 33.92688	+19 48 04.0212	1050-19140204	316.141362	+19.801117			15.5	14.6	1953.748

%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	0.37	21 04 33.5568	+19 48 02.520	0165702486	316.13982	+19.80070	0.3	14.30	0.40	1	3	0591	1983.612

%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

Full	_r arcsec	_RAJ2000 [****ClosingBrace(s)Inserted****]
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