galactic year

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galactic year

See cosmic year.

Galactic Year


the period of revolution of the sun and the stars closest to it around the center of the Milky Way System. Usually it is this quantity that is considered the period of rotation of the Milky Way System. (The period of revolution varies among stars that are located at different distances from the center of the Milky Way System.) The galactic year is equal to about 180 million earth years.

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Younger, chaotic ring structures, says Schechter, are 1 or 2 galactic years old (a galactic year being one rotation of the galaxy), ranging anywhere from 100 million to 200 million years.