Scope and content The Palomar Observatory Sky Survey, or POSS1, consists of photographic plates depicting the northern sky as observed at the Palomar Observatory in Pasadena, California. Each of the 937 fields covers approximately 6 degrees square from +90° to -33° declination. Each field was photographed twice, once on a blue plate (Kodak type 103a-O) and once on a red plate (Kodak type 103a-E), in combination with a red Plexiglas 2444 filter, peaking at 6563 A°. The limiting magnitude on the plates is +22. ...