Astronomy Picture of the Day

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

October 19, 1995
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Globular Cluster M5
Credit: Anglo-Australian Telescope photograph by David Malin
Copyright: Anglo-Australian Telescope Board

Explanation: The globular cluster M5, pictured above, contains roughly 100,000 stars. These stars formed together and are gravitationally bound. Stars orbit the center of the cluster, and the cluster orbits the center of our Galaxy. So far, about 160 globular clusters are known to exist in a roughly spherical halo around the Galactic center. Globular clusters do not appear spherically distributed as viewed from the Earth, and this fact was a key point in the determination that our Sun is not at the center of our Galaxy. Globular clusters are very old. There is a straightforward method of determining their age, and this provides a very interesting lower limit on the age of our universe of about 14 billion years.

Tomorrow's picture: Asteroid Gaspra's Best Face

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Authors & editors: Robert Nemiroff (GMU) & Jerry Bonnell (USRA).
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