Palomar Observatory Sky Survey

The Palomar Observatory Sky Survey (POSS) was a 1950s survey using the Palomar 48 Inch Telescope at Palomar Observatory, that produced a set of photographic plates (the POSS plates) covering the 60% of the sky visible from the observatory. A printed version was available to astronomers to assist in observation, and a number of astronomers produced catalogs by inspecting them for object types of specific interest.

The Second Palomar Observatory Sky Survey (aka Palomar Observer Sky Survey II or POSS-II) is a repeat done in the 1980s and 1990s with the same telescope but with technological upgrades. The Palomar Digital Sky Survey (DPOSS) is a digitization of the POSS-II photographic plates.