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May 2005

A Galactic Fossil

M13 is one of the fuzzy blobs cataloged by the French comet hunter Charles Messier back in the late 1700s. messier did not care what objects were in his catalog; he just wanted to note objects that could be confused with comets. The resulting Messier catalog is a wonderful collection of star clusters, galaxies, and nebulae that provides numerous targets for the amateur astronomer.

M13, in the constellation Hercules, is one of the largest of over 100 globular clusters in our Galaxy. Located about 25,000 light-years away, it contains about half a million stars packed into a ball only tens of light years in diameter. Globular cluseters formed in the earliest days of our Galaxy and contain some of the oldest stars in the Universe. The age of the stars in these closters thus provides an important constraint on our estimates of the age of the entire Universe.