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Hubble sequence
Galaxy morphological classification scheme advocated by Edwin Hubble / From Wikipedia, the free encyclopedia
The Hubble sequence is a morphological classification scheme for galaxies published by Edwin Hubble in 1926.[1][2][3][4] It is often colloquially known as the Hubble tuning-fork diagram because the shape in which it is traditionally represented resembles a tuning fork. It was invented by John Henry Reynolds and Sir James Jeans.[5]
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The tuning fork scheme divided regular galaxies into three broad classes – ellipticals, lenticulars and spirals – based on their visual appearance (originally on photographic plates). A fourth class contains galaxies with an irregular appearance. The Hubble sequence is the most commonly used system for classifying galaxies, both in professional astronomical research and in amateur astronomy.