44 million stars and counting: astronomers play Snap and remap the sky

28 November 2013 - Tens of millions of stars and galaxies, among them hundreds of thousands that are unexpectedly fading or brightening, have been catalogued properly for the first time. Professor Bryan Gaensler , Director of the ARC Centre of Excellence for All-sky Astrophysics ( CAASTRO ) based in the School of Physics at the University of Sydney, Australia, and Dr Greg Madsen at the University of Cambridge, undertook this formidable challenge by combining photographic and digital data from two major astronomical surveys of the sky, separated by sixty years. The new precision catalogue has just been published in The Astrophysical Journal Supplement Series. It represents 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. Professor Gaensler and Dr Madsen began by re-examining a collection of 7400 old photographic plates, which had previously been combined by the US Naval Observatory into a catalogue of more than one billion stars and galaxies. The astronomers then set out to painstakingly match all the objects in this catalogue with more modern measurements from the Sloan Digital Sky Survey. Using very stringent criteria to be absolutely sure of a match, Professor Gaensler and Dr Madsen produced a final catalogue of 44 million stars and galaxies that had definitely been seen twice: both in old photographs and with modern cameras.