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On the Cover Issue 46, Spring 2012

Astronomers used the Galaxy Evolution Explorer (GALEX) telescope to take this deep image in ultraviolet light of the sprawling spiral galaxy M81, hoping to learn where it kept its hot stars. Hot stars emit more ultraviolet than cool stars, and are frequently associated with young, open clusters of stars and energetic star-forming regions. Less than 100 million years old, the young stars are blue and are well separated from the older, yellowish stars of the galactic core. M81, visible through a small telescope, spans about 70,000 light years and lies about 12 million light years away toward the constellation of the Great Bear (Ursa Major).

Photo Credit: NASA/JPL-Caltech

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