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Palomar Observatory Sky Survey (POSS) A photographic star atlas of the northern sky and part of the southern sky to a declination of –33°. It was prepared at the Mount Palomar Observatory, California, with the collaboration of the National Geographic Society, using the 48-inch Oschin Schmidt telescope. It was released 1954–58. It consisted of 935 pairs of photographic prints: one of each pair was made from an exposure on a blue-sensitive plate, the other was made from an exposure taken through a red filter. This survey, known as POSS-I, included stars to a limiting magnitude of 21 (20 in the southernmost plate). A second survey of the northern sky, known as POSS-II, was carried out in the 1980s with an upgraded version of the Palomar Oschin Schmidt, using much improved film. Objects four times as faint as those photographed by POSS-I were recorded. Identifications on POSS prints can be made using a set of labeled transparent overlays, prepared at Ohio State University by R. Dixon and published in 1981. The prints from both POSS-I and POSS-II are being converted to computerized digital format and are becoming accessible over the World Wide Web and as part of the Digitized Sky Survey. See also Southern Sky Survey.