Alfred Harrison Joy

Alfred Harrison Joy ( born September 23, 1882 in Greenville, Illinois, † 18 April 1973 in Pasadena, California ) was an American astronomer.

After earning his bachelor's degree from Greenville College in Illinois and a master's in physics at Oberlin College, Joy taught ten years at the American University of Beirut and became a professor and director of its observatory. During this time he built during visits to various European and American observatories on contacts with astronomers as Henry Norris Russell. The First World War prevented his return from a 1915 trip to the U.S. to Beirut, after which he worked until his retirement in 1948 at Mount Wilson Observatory stay and now scientifically active.

At Mount Wilson Observatory, he dealt first with solar observations, but turned later in 1916 his main field of spectroscopy of stars, too. In extensive observation projects, he and his colleagues measured radial velocities, spectroscopic parallaxes, determined by the distance of stars and studied variable stars, such as Mira. He identified the class of T Tauri stars. Based on its radial velocity measurements, he examined the rotation and structure of the Milky Way.

Joy was in 1931 and 1939, President of the Astronomical Society of the Pacific, and from 1949 to 1952 president of the American Astronomical Society. In 1950 he received the Bruce Medal. A lunar crater is named after him.