The First U.S. Naval Observatory Robotic Astrometric Telescope Catalog

URAT1 is an observational, astrometric catalog covering most of the δ −15° area and a magnitude range of about R = 3–18.5. Accurate positions (typically 10–30 mas standard error) are given for over 228 million objects at a mean epoch around 2013.5. For the over 188 million objects matched with the Two Micron All Sky Survey (2MASS) point-source catalog proper motions (typically 5–7 mas yr–1 standard errors) are provided. These data are supplemented by 2MASS and AAVSO Photometric All-Sky Survey (APASS) photometry. Observations, reductions, and catalog construction are described, together with results from external data verifications. The catalog data are served by CDS, Starsbourg (I/329).