PMM - The Whole Sky

This is an image of the sky as tabulated in the USNO-A2.0 catalog. The catalog was derived from measurement of all the stars visible on the photographic plates which resulted from three major photographic surveys of the sky: the Palomar Optical Sky Survey made in the 1950s (POSS-I), the Science Research Council (SRC)-J, and the Euopean Southern Observatory (ESO)-R. The original photographic plates which resulted from each of these surveys were digitized with the PMM. The star measurements from all these plates were put on the International Celestial Reference Frame (ICRF), as realized by the USNO ACT catalogue. The resulting catalog contains 526,280,881 stars, each measured in two colors (red and blue.) A more detailed .gif image is viewable, but may take a while to load.

What is shown in this image is the number density of stars, or the number of stars per square degree. Yellow corresponds to the highest density - about 150,000 stars per square degree, and dark blue to the lowest - only 500 stars per square degree. The dense (bright yellow) band across the middle of the image is the Milky Way, or the plane of our own galaxy. Dark areas superimposed on the central band are clouds of dust and gas which obscure some of the stars from our view. The two bright ``blobs'' below and to the right of center are the Magellanic Clouds. The area of increased brightness corresponds to the part of the sky photographed by the two southern hemisphere surveys, both of which reached a fainter limiting magnitude (or stellar brightness.)

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