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.

July 26, 1997

M81 in True Color
Credit: G. Bothun (U. Oregon), courtesy W. Keel (U. Alabama)

Explanation: Here's is a spiral galaxy in true colors. Previously, M81 was shown in two colors only, but M81's real colors are just as dramatic. In the above picture, note how blue the spiral arms are - this indicates the presence of hot young stars and on-going star formation. Also note the yellow hue of the nucleus, indicating am ancient population of stars many billions of years old. M81 is actually a dominant member of a group of galaxies which includes M82 and several other galaxies. Unlike our Local Group of galaxies, large galaxies in the M81 group are actually colliding. It is possible that M81's interaction with M82 create the density waves which generate M81's spiral structure.

Tomorrow's picture: A Very Large Array of Radio Telescopes

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
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