Edwin Hubble employer Mount Wilson Observatory
Career
In 1919, Hubble was offered a staff position at the Carnegie Institution for Science's Mount Wilson Observatory, near Pasadena, California, by George Ellery Hale, the founder and director of the observatory. Hubble remained on staff at Mount Wilson until his death in 1953. Shortly before his death, Hubble became the first astronomer to use the newly completed giant 200-inch (5.1 m) reflector Hale Telescope at the Palomar Observatory near San Diego, California.
Hubble also worked as a civilian for U.S. Army at Aberdeen Proving Ground in Maryland during World War II as the Chief of the External Ballistics Branch of the Ballistics Research Laboratory during which he directed a large volume of research in exterior ballistics which increased the effective firepower of bombs and projectiles. His work was facilitated by his personal development of several items of equipment for the instrumentation used in exterior ballistics, the most outstanding development being the high-speed clock camera, which made possible the study of the characteristics of bombs and low-velocity projectiles in flight. The results of his studies were credited with greatly improving design, performance, and military effectiveness of bombs and rockets. For his work there, he received the Legion of Merit award.Discoveries
Universe goes beyond the Milky Way galaxy
Edwin Hubble's arrival at Mount Wilson Observatory, California, in 1919 coincided roughly with the completion of the 100-inch (2.5 m) Hooker Telescope, then the world's largest. At that time, the prevailing view of the cosmos was that the universe consisted entirely of the Milky Way Galaxy. 
Using the Hooker Telescope at Mount Wilson, Hubble identified Cepheid variables, a standard candle discovered by Henrietta Leavitt. Comparing their apparent luminosity to their intrinsic luminosity gives their distance from Earth. Hubble found Cepheids in several nebulae, including the Andromeda Nebula and Triangulum Nebula. His observations, made in 1924, proved conclusively that these nebulae were much too distant to be part of the Milky Way and were, in fact, entire galaxies outside our own, thus today they are no longer considered nebulae. 
This was first hypothesized as early as 1755 when Immanuel Kant's General History of Nature and Theory of the Heavens appeared. This hypothesis was opposed by many in the astronomy establishment of the time, in particular by Harvard University–based Harlow Shapley. Despite the opposition, Hubble, then a thirty-five-year-old scientist, had his findings first published in The New York Times on November 23, 1924, then presented them to other astronomers at the January 1, 1925, meeting of the American Astronomical Society. Hubble's results for Andromeda were not formally published in a peer-reviewed scientific journal until 1929.
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