Edwin Hubble (1889-1953), the American astronomer and cosmologist, photographed in 1924 at the Mount Wilson Observatory, where he worked for most of his life. In 1923, while using the 100-inch telescope there, he observed Cepheid variable stars in the Andromeda galaxy. This and further work proved the existence of galaxies outside of our own. He went on to introduce the classification of galaxies as spirals, barred spirals and ellipticals. In 1929 he announced Hubble's law, that is, that the galaxies are moving apart at a rate that increases with their distance.