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Andromeda Galaxy

or M31

Great spiral galaxy in the constellation Andromeda. It is the nearest spiral galaxy outside the Milky Way Galaxy and one of the few visible to the unaided eye, appearing as a milky blur. About 2 million light-years from Earth, it has a diameter of about 200,000 light-years, which makes it the largest galaxy in the Local Group. For centuries astronomers considered it part of the Milky Way; only in the 1920s did Edwin Hubble determine conclusively that it was a separate galaxy.

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