Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

April 26, 1999
See Explanation.  Clicking on the picture will download 
 the highest resolution version available.

USNO-A2.0 Catalog: A Digital Sky
Credit: PMM Team, USNO Flagstaff Station

Explanation: Here lie 526,230,881 of the brightest stars known. The US Naval Observatory has deployed their monster Precision Measuring Machine to digitize photographic plates covering the whole sky and creating the above map. Yellow corresponds to 150,000 stars per square degree, while dark blue corresponds to only 500 stars per square degree. (For comparison, the Full Moon takes up about 1/4 of a square degree.) The most striking feature on this whole sky projection is the central disk of our Milky Way Galaxy, which stretches across the middle. Dark dust lanes are evident there by the great number of stars they obscure. The two bright spots seen south of the Milky Way's disk are the neighboring Magellanic Cloud galaxies. Anyone can order a free copy of this data, but not everyone can fit data from all 526,230,881 stars on their hard-drive.

Tomorrow's picture: A New Comet Brightens

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
A service of: LHEA at NASA/ GSFC
& Michigan Tech. U.