Edwin Powell Hubble

Edwin Powell Hubble (November 20, 1889, Marshfield, Missouri – September 28, 1953, San Marino, California) was an American astronomer who is considered the founder of extragalactic astronomy and who provided the first evidence of the expansion of the universe.

Hubble earned an undergraduate degree in both mathematics and astronomy at the University of Chicago in 1910. Upon graduation Hubble left astronomy and started a law study as a Rhodes Scholar at the University of Oxford (B.A., 1912). He joined the Kentucky bar in 1913 but soon gave up his practice being bored with law. He returned to the University of Chicago and earned a Ph.D. in astronomy (1917), while doing research at Yerkes Observatory. After serving in World War I, Hubble joined the staff at the Mount Wilson Observatory near Pasadena, California, upon invitation of the astronomer George Ellery Hale. Here he began to make discoveries concerning extragalactic phenomena.

Soon Hubble discovered that not all nebulae belong to the Milky Way Galaxy, the star system to which the Sun belongs. Using the Hooker Telescope at Mt. Wilson and applying relationships among distance, apparent magnitude, and absolute magnitude, Hubble determined that certain spiral nebulae, notably the Andromeda Nebula, contain a kind of stars,  Cepheid variables, that are are in other galaxies than the Milky Way. This discovery, announced in 1924, forced astronomers to revise their ideas about the cosmos.

Soon after discovering the existence of other galaxies than the Milky Way, Hubble undertook the task of classifying them according to their shapes (1926) and exploring their stellar contents and brightness patterns. In studying the galaxies, Hubble made his second remarkable discovery—namely, that these galaxies are apparently receding from the Milky Way and that the further away they are, the faster they are receding (1927). The implications of this discovery were immense. The universe, long considered static, was expanding; and, even more remarkably, as Hubble discovered in 1929, the universe was expanding in such a way that the ratio of the speed of the galaxies to their distance is a constant now called Hubble's constant. In 1929 Hubble and Humason formulated the empirical redshift distance law of galaxies, nowadays termed simply Hubble's law. Hubble discovered the asteroid 1373 Cincinnati on August 30, 1939.

For his achievements in astronomy, Hubble received many honors and awards. Among his publications are Red Shifts in the Spectra of Nebulae (1934), The Realm of the Nebulae (1936), The Observational Approach to Cosmology (1937), and The Hubble Atlas of Galaxies (published posthumously, 1961, and edited by Allan Sandage).