National Geographic Society – Palomar Observatory Sky Survey

The Palomar Observatory Sky Survey ( POSS ) was the most important photographic survey of the northern and equatorial sky in the second half of the 20th century.


The first Palomar Observatory Sky Survey was conducted with support from the National Geographic Society since 1948 from the California Institute of Technology and completed in 1958. Recording instrument was the large Schmidt telescope ("Big Schmidt ," primary mirror 180 cm, 120 cm clear aperture, focal length 300 cm) at the Mount Palomar Observatory. The survey extends over large parts of the Südsternhimmels and shows all the stars and galaxies up to about the 22 size class.

The individual photographic plates each cover about 6 ° x 6 ° from the sky. Each field was observed twice, once with a blue-sensitive Kodak 103a- O photographic plate and one with a red-sensitive Kodak 103a -E plate. Thus, the POSS also contains information about the color of the observed celestial objects, which can be very roughly estimated, for example, for stars of spectral type. The sensitivity depends on the shooting conditions of each plate, in the blue about the 22 class size has been reached. The original POSS- survey covered the area from the north celestial pole to a declination of -33 °. In later years, the POSS called Whiteoak extension was a southern complement to 100 red-sensitive photographic plates, expanded up to a declination of -45 °. Due to the SERC / ESO survey for the southern sky, the ESO / SERC Southern Sky Survey ( cover from -20 ° to south celestial pole ), finally, the entire sky was covered.

The first POSS comprises 936 pairs of plates and is today with its all-sky coverage of major importance. Only in some areas has been obtained with the Sloan Digital Sky Survey a much better all-sky survey. The POSS is the source for a variety of catalogs of various astronomical object classes and was often the starting point for detailed studies of individual objects. At many observatories paper copies of the POSS were an important tool, in some places even more accurate copies on glass plates. Since 1994, a digitized version ( Digitized Sky Survey ) is available, which is accessible via several data centers across the web. He still provides an important basis for astronomical analysis and discoveries - for example, stellar statistics, pre-and post -novae, variable stars, and also for the orbit determination of asteroids and comets and for the study of galaxy clusters.


Since the 1980s, was carried out with instrumental improvements and better photographic plates a second Palomar Observatory Sky Survey ( POSS II). As part of the POSS II the sky fields were included not only blue-sensitive (Kodak IIIaJ ) and rotenpfindliche (Kodak IIIaF ) photographic plates, but also in the near infrared (Kodak IVN ). This survey is important not only because of their better data, but also in combination with the first POSS for the study of stellar motions and variable objects. The POSS II consists of 3 × 897 plates and was completed in 1999. Since the fields overlap more than the first POSS was covered despite the high number of photographic plates, only the northern sky to the celestial equator. The gap between POSS -II and ESO / SERC Southern Sky Survey was supported by the SERC -EJ atlases ( blue-sensitive plates) and SERC -ER ( red-sensitive plates) in Deklinationsbereich between 0 ° and -15 ° closed.

The POSS- II was amplified by ESO between 1994 and 2001 on film and distributed. Due to the high price of the POSS- II is not nearly as common as the first POSS, but is found in all major observatories and astronomical institutes.

From the digitized POSS- plates of the first and second generation, and the southern addition to it, the most extensive star catalog, the USNO -B, and the Digitized Sky Survey was compiled II (DSS -2) at the U.S. Naval Observatory. Both works list the positions and brightnesses of over a billion stars and galaxies.