An all-sky catalogue of positions and proper motions of stars between 8th and 16th magnitudes produced by the US Naval Observatory; proper motions are derived by reference to older catalogues. Observations of the southern hemisphere were made at Cerro Tololo Inter-American Observatory in Chile with a 0.2-m astrograph in 1998–2001. The telescope was then moved to the US Naval Observatory’s Flagstaff Station in Arizona to observe the northern sky. Intermediate data releases, UCAC1 and UCAC2, were made in 2000 and 2003. Observations ended in 2004. The first all-sky version, UCAC3, containing 100 766 420 stars to 16th magnitude, was published in 2009. The final catalogue, UCAC4, was released in 2012, containing 113 780 093 stars.

http://www.usno.navy.mil/USNO/astrometry/optical-IR-prod/ucac Official catalogue web page.