Note that the errors on the
proper motions are large (∼50mas/yr), and therefore the positions
computed at an epoch different from 1991.25 have a large (∼0.4")
The Tycho Epoch Photometry data can
be accessed from the morePhoto column
(includes VT, BT and Hp photometric data for Hipparcos stars
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 (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.
Note: The Guide Star Catalog has been constructed to support the
operational need of the Hubble Space Telescope.
It contains over 25 million positions for about 19 million
objects, of which more than 15 million are classified as stars.
The version 1.2 is a new astrometric reduction which results in
absolute position errors about 0.3-0.4 arcsec.
(see GSC pages at URL http://www-gsss.stsci.edu/gsc/gsc.html)
The USNO-B Catalog presents positions, proper motions,
magnitudes un blue, red and infrared, as well as star/galaxy estimators
for 1,045,175,762 objects derived from 3,648,832,040 separate observations.
The data were taken from scans of 7,435 Schmidt plates
taken from various sky surveys during the last 50 years.
USNO-B1.0 catalog was created by Dave Monet and collaborators
Note that the star/galaxy estimators may be mixed up
in dense regions.
Note: More recent versions available: UCAC3 (I/315) and UCAC4 (I/322); see also the UCAC home page at http://ad.usno.navy.mil/ucac/
The Naval Observatory Merged Astrometric Dataset (NOMAD) contains
astrometric and photometric data for over 1 billion stars derived from
the Hipparcos (I/239), Tycho-2 (I/259), UCAC2 (I/289), and USNO-B1.0
(I/284) catalogs for astrometry and optical photometry, supplemented
by 2MASS (II/246) near-infrared photometry.
An efficient remote query program findnomad1 is
available in the cdsclient
package, for Unix/Linux platforms
Note: This version of the
has no proper motions, but the limits on brightness which existed on
GSC2.2 (F<18.5, Bj<19.5) were removed.
Note: The limiting magnitude is about 15.2 in the GSC photometric system.