UCAC

UCAC, the United States Naval Observatory CCD Astrograph Catalog, is an all-sky astrometric catalog that provides precise positions and proper motions for a large sample of stars. It is designed to serve as a high-accuracy reference for astrometry and to aid the calibration of wide-field surveys.

Content and scope: UCAC contains positions, proper motions, and photometric information for tens of millions of stars, with magnitudes roughly in the 8 to 16 range. The catalog entries are referenced to the J2000.0 epoch and linked to other major catalogs to facilitate cross-identification.

Construction and data quality: The catalog was produced using a dedicated CCD-based astrograph and a data-processing pipeline that measured precise stellar positions from all-sky imaging. By combining modern CCD measurements with older astrometric data, UCAC provides proper motions for many stars and achieves typical positional accuracies on the order of tens of milliarcseconds for brighter stars, decreasing toward the fainter end.

Uses and significance: UCAC has been widely used to anchor the celestial reference frame, calibrate wide-field surveys, and enable reliable cross-matching across astronomical datasets. It supports stellar and Galactic studies and serves as a complement to space-based astrometric missions.

Status and lineage: UCAC is one of several major all-sky astrometric catalogs produced in the early 21st century. Its releases have evolved to improve accuracy, extend magnitude coverage, and enhance compatibility with other catalogs, including Gaia.