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	3.900	06 04 28.37208	-20 20 27.0708	0675-02617687	091.118217	-20.340853			19.7	18.2	1981.419
2	4.962	06 04 28.42008	-20 20 27.9528	0675-02617701	091.118417	-20.341098			19.6	19.1	1953.863
3	5.059	06 04 28.26480	-20 20 29.6808	0675-02617656	091.117770	-20.341578			17.6	17.5	1981.419
4	14.656	06 04 28.02888	-20 20 10.3632	0675-02617567	091.116787	-20.336212			19.5	18.2	1981.419
5	21.167	06 04 27.99408	-20 20 46.0032	0675-02617555	091.116642	-20.346112			14.7	14.4	1953.863

%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	20.88	06 04 27.9672	-20 20 45.672	0594000856	091.11653	-20.34602	0.2	14.88	0.31	0	3	01O2	1982.868

%0a%22>ts_init('!ext/gsc1.2.exe_2');">\Endscript

Note: The GSC-ACT (or GSC1.3) is a recalibration of the GSC1.1, the catalogue constructed to support the operational need of the Hubble Space Telescope, with the ACT, the combination of the Astrographic Catalogue and the Tycho catalogue derived from the Hipparcos mission; see http://www.projectpluto.com/gsc_act.htm for more details about this recalibration.

Full	_r arcsec	_RAJ2000 "h:m:s"	_DEJ2000 "d:m:s"	GSC	RAJ2000 deg	DEJ2000 deg	PosErr arcsec	Pmag mag	e_ mag	n_	Class	Epoch yr
1	20.76	06 04 27.9744	-20 20 45.564	0594000856	091.11656	-20.34599	0.2	14.90	0.32	0	3	1982.868

%0a%0a%3cP%3e%0a%3cFONT%20SIZE=%27-1%27%3e%3cEM%3e%3cFONT%20COLOR=%27#0000FF%27>%3cB%3eNote:%20The%20construction%20of%20the%20%0a%3cB%3eGSC-II%20%0ais%20still%20in%20progress:%20this%0aversion%20has%20no%20proper%20motions,%20and%20the%20magnitude%20limits%20are%2018.5%20in%20F%20%28red%29%0aand%2019.5%20in%20J%20%28blue%29.%20The%20data%20are%20%3cB%3e%3cFONT%20COLOR=%27#0000CD%27>copyrighted,%20check%20%0athe%20%3cB%3edata%20use%20Policy.%0a%3cP%3e%0a

Full	_r arcsec	_RAJ2000 "h:m:s"	_DEJ2000 "d:m:s"	GSC2.2	RA(ICRS) deg	DE(ICRS) deg	Epoch yr	Rmag mag	e_ mag	Bjmag mag	e_ mag	Class	a pix	e
1	20.920	06 04 27.98352	-20 20 45.7404	S1001003121	091.116598	-20.346039	1992.074	13.91	0.26	14.16	0.26	3	10.10	0.46

%0a%0a%3cP%3e%0a%3cFONT%20SIZE=%27-1%27%3e%3cEM%3e%3cFONT%20COLOR=%27#0000FF%27>%3cB%3eNote:%20The%20%3cB%3eUSNO-B%20Catalog%20presents%20positions,%20proper%20motions,%20%0amagnitudes%20un%20blue,%20red%20and%20infrared,%20as%20well%20as%20star/galaxy%20estimators%0afor%201,045,175,762%20objects%20derived%20from%203,648,832,040%20separate%20observations.%0aThe%20data%20were%20taken%20from%20scans%20of%207,435%20Schmidt%20plates%0ataken%20from%20various%20sky%20surveys%20during%20the%20last%2050%20years.%3cBR%3e%0aUSNO-B1.0%20catalog%20was%20created%20by%20Dave%20Monet%20and%20collaborators%0aat%20http://www.nofs.navy.mil/data/fchpix/%20%3cBR%3e%0a%3cB%3e%3cFONT%20COLOR=%27#EE0000%27>%20Note%20that%20the%20star/galaxy%20estimators%20may%20be%20mixed%20up%0a%20in%20dense%20regions.%0a%3cP%3e%0a

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