Hubble, Edwin Powell (1889–1953)
Edwin Hubble was an American astronomer whose observations proved that galaxies are "island universes," not nebulae inside our own galaxy. His greatest discovery was the linear relationship between a galaxy's distance and the speed with which it is moving, now known as the Hubble law.
Upon graduation from the University of Chicago, Hubble won a Rhodes scholarship and earned a law degree at Oxford University. After obtaining his doctorate he spent his career, aside from army service in both world wars, at Mount Wilson Observatory where he used the 100-inch (2.5m) telescope.
In 1923 to 1925 he identified Cepheid variables in the "nebulae" NGC 6822, M31 (the Andromeda Galaxy), and M33 (the Triangulum Galaxy) and proved conclusively that they are outside the Galaxy. His investigation of these and similar objects, which he called extragalactic nebulae and which astronomers today call galaxies, led to his now-standard classification system of elliptical, spiral, and irregular galaxies, and to the proof that they are distributed uniformly out to great distances. Hubble measured distances to galaxies and, with Milton Humason, extended Vesto Slipher's measurements of their redshifts. In 1929 he published the velocity-time relation which, taken as evidence of an expanding universe, is the basis of modern cosmology; the constant in this relation is called the Hubble constant.
The Hubble Space Telescope is also named in his honor.