The UCAC4 catalog (Fourth U.S. Naval Observatory CCD Astrograph Catalog) is an all-sky star catalog with about 113 million stars covering mainly the mag 8 to mag 16 magnitude range. It provides accurate astrometric and photometric information.  Phoranso uses this catalog both for astrometric measurements to calculate the position of the stars in your images and for photometric measurements to extract precise brightness information in various wavelengths (bands) for stars in your images. 


UCAC4 contains about 113 million stars with astrometric and magnitude information in a single bandpass between V and R. These data are supplemented by 2MASS photometric data for about 110 million stars and 5-band (B,V,g,r,i) photometry from the APASS (AAVSO Photometric All-Sky Survey) for over 50 million stars.