Off to War
While finishing up the work for his doctorate in 1917, George Ellery Hale had invited Hubble to join the staff of Mount Wilson Observatory in Pasadena, California. Hubble spent an entire night finishing his thesis, completed the oral defense of his dissertation the following morning, and then proceeded to enlist in the U.S. Army a few days later. He sent a telegraph to Hale, saying: "Regret cannot accept your invitation. Am off to the war."
Hubble served as a captain in the 343rd Infantry, 86th Division, and eventually earned the rank of major. He was commissioned to France, where he spent time as a field and line officer. Returning to the United States in the summer of 1919, Hubble traveled immediately to the Mount Wilson Observatory and accepted a position there. Founded by Hale in Pasadena in 1904, Mount Wilson Observatory was, in Hubble's time, the center of observational work on astrophysics. It had the two largest and most powerful telescopes in the world in the 60-inch and 100-inch Hooker reflectors.