National Geographic Society – Palomar Observatory Sky Survey
The National Geographic Society – Palomar Observatory Sky Survey (NGS-POSS) was a major astronomical survey, that took almost 2,000 photographic plates of the night sky. It was conducted at Palomar Observatory, California, United States, and completed by the end of 1958.
Observations
The photographs were taken with the 48-inch Samuel Oschin telescope at Palomar Observatory, and the astronomical survey was funded by a grant from the National Geographic Society to the California Institute of Technology. Among the primary minds behind the project were Edwin Hubble, Milton L. Humason, Walter Baade, Ira Sprague Bowen and Rudolph Minkowski. The first photographic plate was exposed on November 11, 1949. 99% of the plates were taken by June 20, 1956, but the final 1% was not completed until December 10, 1958.
The survey utilized 14-inch square photographic plates, covering about 6° of sky per side (approximately 36 square degrees per plate). Each region of the sky was photographed twice, once using a red sensitive Kodak 103a-E plate, and once with a blue sensitive Kodak 103a-O plate. This allowed the color of celestial objects to be recorded.
Astronomical survey
An astronomical survey is a general map or image of a region of the sky which lacks a specific observational target. Alternatively, an astronomical survey may comprise a set of many images or spectra of objects which share a common type or feature. Surveys are often restricted to one band of the electromagnetic spectrum due to instrumental limitations, although multiwavelength surveys can be made by using multiple detectors, each sensitive to a different bandwidth. Surveys have generally been performed as part of the production of an astronomical catalog.
Scientific value
Sky surveys, unlike targeted observation of a specific object, allow astronomers to catalogue celestial objects and perform statistical analyses on them without making prohibitively lengthy observations. In some cases, an astronomer interested in a particular object will find that survey images are sufficient to entirely obviate the need for telescope time.
Surveys also help astronomers obtain observation time on larger, more powerful telescopes. If the astronomer can show a telescope scheduling committee that previous observations support his or her hypothesis, he or she is more likely to be given a chance to make more detailed observations.
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