The National Geographic Society-Palomar Observatory Sky Survey, published in 1954, was a complete photographic survey of the sky from the north celestial pole southward to declination - 27¡. The survey, sponsored by the National Geographic Society and the California Institute of Technology, required about 8 years of observing time, using Palomar's 48-in (122-cm) Oschin Telescope, a Schmidt telescope.Astronomers obtained 879 pairs of plates; each pair consisted of a blue exposure and an exposure using red-sensitive plates and a red filter. Both exposures reached the limit of about magnitude 20. Each 35-cm-square (14-in-square) plate covered an area of sky about 7 degrees square. The atlas derived from this survey, as distributed to astronomers, is in the form of negative photographic copies. The survey is extremely valuable for identifying faint optical objects, such as quasars, radio sources, and X-ray sources. The survey plates have revealed many peculiar astronomical objects. Other discoveries include many distant clusters of galaxies, several nearby dwarf galaxies, and several distant globular clusters.Using Schmidt telescopes in Chile and Australia, astronomers are completing a survey of the southern sky. A new Palomar northern sky survey, funded only in part by the National Geographic Society and taking advantage of new photographic technology, was begun in 1986.