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A new observational catalog from USNO is available

URAT is a follow-up project to the successful UCAC project using the same astrograph but with a much larger focal plane array.

Longer integration times and more sensitive, backside CCDs allowed for a substantial increase in limiting magnitude, resulting in about 4-fold increase in the average number of stars per square degree as compared to UCAC.

Additional observations with an objective grating largely extend the dynamic range to include observations of stars as bright as about 3rd magnitude. Multiple sky overlaps per year result in a significant improvement in positional precision as compared to UCAC.

  • Observational catalog, i.e. mean positions of stars at mean epoch of URAT observing (between 2012.3 and 2014.6), on the International Celestial Reference System (ICRS).
  • Covering the about R = 3 to 18.5 magnitude range with positional precisions of 5 to 40 mas depending on observing history and brightness of stars.
  • Covering most of the northern hemisphere and in some areas as far south as -24.8 deg Dec (Pluto field).
  • Observed in a single bandpass (680 to 750 nm = between R and I).
  • Constructed from 2 years of operations of the astrograph at the Naval Observatory Flagstaff Station (NOFS), with multiple sky overlaps per year of regular exposures (240 sec and 60 sec) and objective grating exposures (30,20,10 sec)
  • Small systematic errors due to higher quality of the CCDs as compared to UCAC (expected error floor is about 5 to 10 mas)
  • URAT1 is supplemented by preliminary proper motions derived exclusively from 2-epoch URAT1 and Two Micron All Sky Survey (2MASS) data (at around epoch 2000) resulting in proper motion errors of typically 5 to 8 mas/yr.
  • Contains 228 million objects (mostly stars) of which 188 million are common to 2MASS
  • Photometry from 2MASS and American Association of Variable Star Observers Photometry All-Sky Survey (APASS) is added for stars in common

Access the catalog from Vizier

Build a local catalog for Skychart

Download the data, software and documentation from

In the “access” directory compile the v1dump program:

en/news/urat1_catalog.1429815601.txt.gz · Last modified: 2015/11/06 20:35 (external edit)