Palomar Observatory Sky Survey

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The Palomar Observatory Sky Survey (POSS , after the Palomar Observatory ) 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 by the California Institute of Technology since 1948 , with support from the National Geographic Society , and completed in 1958. Was recording instrument the big Schmidt Telescope ( "Big Schmidt" primary mirror 180 cm free aperture 120 cm, focal length 300 cm) on Mount Palomar - Observatory . The survey also covers large parts of the southern sky and shows all stars and galaxies up to about the 22nd  magnitude .

The individual photo plates each cover about 6 ° × 6 ° in the sky. Each area was observed twice, once with a Kodak 103a-O blue-sensitive photographic plate and once with a Kodak 103a-E red-sensitive plate. As a result, the POSS also contains information about the color of the celestial objects observed . B. for stars the spectral type can be estimated very roughly. The sensitivity depends on the recording conditions of the individual plate; in the blue, the 22nd size class was reached.

The original POSS survey covered the area from the north celestial pole to a declination of −33 °. In later years, the POSS was expanded to include 100 red-sensitive photo plates, the Whiteoak extension , up to a declination of −45 ° with a southern addition . The ESO / SERC survey of the southern sky, the ESO / SERC Southern Sky Survey (coverage from −20 ° to the south celestial pole), finally covered the entire sky.

The first POSS comprised 936 plate pairs and is still of great importance today due to its complete sky coverage. A significantly better sky survey was only obtained in some areas with the Sloan Digital Sky Survey . The POSS is the source for many catalogs of various astronomical object classes and was often the starting point for detailed investigations of individual objects.

At many observatories, paper copies of the POSS were an important tool, and in some places more precise copies on glass plates were also used. A digitized version has also been available since 1994 ( Digitized Sky Survey ), which can be accessed via various data centers on the web. It still provides an important basis for astronomical analyzes and discoveries - e.g. B. Stellar statistics , pre- and post novae , variable stars , also for the orbit determination of asteroids and comets and for the study of galaxy clusters .


Since the 1980s, a second Palomar Observatory Sky Survey (POSS II) has been carried out with instrumental improvements and better photographic plates. In its frame, the sky fields were not only recorded on blue-sensitive (Kodak IIIaJ) and red-sensitive (Kodak IIIaF) photo plates, but also in the near infrared (Kodak IVN). This survey is not only important because of its better data, but in combination with the first POSS also for the investigation of star movements and changing objects.

The POSS II consists of 3 × 897 plates and was completed in 1999. Since the fields overlap more than with the first POSS, only the northern sky up to the celestial equator was covered despite the high number of photo plates. The gap between POSS II and the ESO / SERC Southern Sky Survey was closed in the declination range between 0 ° and −15 ° by the atlases  SERC-EJ (blue-sensitive plates) and SERC-ER (red-sensitive plates).

The POSS-II was reproduced on film material and distributed by ESO between 1994 and 2001 . Due to its high price, the POSS II is by far not as widespread as the POSS I, but it can be found in all major observatories and astronomical institutes.

From the digitized plates of POSS I and POSS II as well as the southern addition to it, the US Naval Observatory has compiled the most extensive star catalog to date , the USNO-B and the Digitized Sky Survey II (DSS-2). Both works record the positions and brightnesses of over a billion stars and galaxies.

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