After graduating, Joy went on to work at the
American University of Beirut in the Syrian Protestant College as a professor of astronomy and the director of the observatory. He was forced to return to the U.S. in 1915 because of
World War I. In the United States, he worked at the
Mount Wilson Observatory from 1915 to 1952. There, he and his colleagues ascertained the
spectral type,
absolute magnitude, and stellar distance of over 5,000 stars. Joy also initially defined the
T-Tauri type star. He studied the
Doppler displacement of the spectral lines of stars to determine their radial velocities deducing a star's absolute dimensions, masses, and the orbital elements of some specific stars. He won the
Bruce Medal in 1950. He was president of the
Astronomical Society of the Pacific in 1931 and 1939. ==References==