Star Catalogs for Astrometrica

Distribution of stars in the USNO-A2.0 catalog (Source: USNO)

UCAC 3
Observations for the USNO CCD Astrograph Catalog, or UCAC, started in early 1998 and were completed in 2004. With these observations, the UCAC is the first modern high-density, full-sky star catalog that is not based on photographic images of the sky, but on recent CCD observations. After two intermediate releases, which did not cover the whole sky, the final UCAC 3 catalog was released in 2009.
The UCAC 3 includes positions, proper motions and magnitudes for 100,766,420 objects. Reference star positions in UCAC 3 are accurate to about 0.02" for brighter stars (10^mag to 14^mag), and a precision better than 0.1" is expected at the limiting magnitude of 16^mag. Magnitudes have been measured in one single, non-standard color, but the catalog includes visual and infrared magnitudes from other sources.
Astrometrica can access a local copy of the UCAC 3, or query VizieR to download reference star data.

USNO-B 1.0
The USNO-B 1.0 catalog is the successor of the USNO-A2.0 (see below) and contains positions, proper motions and magnitudes for more 1,042,618,261 objects down to 21^mag. It was created by digitizing 7,435 large format Schmidt plates from the first and second generation photographic sky surveys (POSS-I and POSS-II north of -30° declination, ESO, SERC and AAO in the south).
The positions are precise to about 0.2" at current epochs, and magnitudes (in B,R and I) are good to about 0.5^mag.
Astrometrica can access a local copy of the USNO-B 1.0, or query VizieR to download reference star data.

NOMAD
The Naval Observatory Merged Astrometric Dataset (NOMAD) is a merged catalog, with positions and magnitudes for 1.1 billion stars from several source catalogs, including Hipparcos, Tycho-2, UCAC 2, and USNO-B 1.0 (see below). For each star the presumably best astrometric and photometric data were chosen from onw of the source catalogs.
Positions are mainly from the Hipparcos for brighter stars (down to ~10^mag), from UCAC 2 for stars to down to ~16^mag (in those parts of the sky covered by the UCAC 2), and from USNO-B1, down to the limiting magnitude of the latter (21^mag). Positional errors is about 0.015" for stars from Hipparcos, 0.07" for stars from UCAC, and 0.2" fro stars from USNO-B 1.0 (not taking into account any systematic offsets between these catalogs). By setting the lower magnitude limit for the reference stars in the program settings of Astrometrica accordingly, users may control the balance between reference stars with data from the UCAC and the USNO-B.
Due to it's enormous size (100 Gigabytes), the catalog has never been distributed on CD or DVD or some other media, but Astrometrica will automatically query VizieR to download NOAMD reference star data.

CMC-14
The 14. Carlsberg Meridian Catalog is the result of the observations of 96 million stars with the Carlsberg Meridian Telescope on La Palma. It covers the sky between +50° and -30° declination, minus a gap between R.A. 5^h30^m and 10^h30^m for stars south of -15° declination.
Astrometric positions in CMC-14 are precise to 0.05" for bright stars (13^mag or brighter) and to 0.1" for stars at the limiting magnitude of 16^mag. There are no proper motions, but as the catalog positions were derived from recent CCD observations (1999-2005), the positions are still very precise at current epochs. The catalog includes red magnitudes, with errors from only 0.025^mag for bright stars (13^mag or brighter) to 0.17^mag at the limiting magnitude of 16^mag. The photometric data is therefore much better then that of most other astrometric catalogs.
Astrometrica can access a local copy of the CMC-14, or query VizieR to download reference star data.

USNO-A 2.0, USNO-SA 2.0 and UCAC 2
The USNO-A2.0 and USNO-SA2.0 (a subset of the USNO-A 2.0) have effectively been replaced by the USNO-B1.0 catalog. Use of these catalogs is no longer recommended, however, Astrometrica can still access local copies of these catalogs, which have originally been distributed on CD-ROM.
Similarly, the UCAC 2 has been replaced by the UCAC 3. Access to UCAC 2 data in Astrometric has not been disabled, so users who have a copy of the the UCAC 2 may continue to use it if they choose to do so.