By combining photographic and digital data from the US Naval Observatory-B and Sloan Digital Sky Survey DR9 catalogues, astronomers have made one of the most comprehensive and accurate compilations of stars and galaxies ever produced, covering 35 percent of the sky and using data going back as far as 1949. About 44 million stars and galaxies, among them hundreds of thousands that are unexpectedly fading or brightening, have been catalogued by astronomers...
