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. Each glass plate negative is fourteen inches square and three thirty-seconds inches thick. These plates are copies of the master set created by the California Institute of Technology under sponsorship of the National Geographic Society between 1948 and 1958.

1874 glass plate negatives.

Also, original sky overlay maps and atlases (1954), reprints, cross references, plate location maps, acetate grids, and material regarding galactic coordinates.