Alfred H. Joy (1882–1973) was an astronomer at the Mount Wilson Observatory from 1915 to 1973 who measured spectroscopic parallaxes and radial velocities of stars and studied variable stars. He invented the T Tauri classification.

After graduating MA from Oberlin College in 1904, 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 the 1st World War.

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 discovered 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.

Dr. Joy was elected an honorary member of the Royal Astronomical Society of Canada on 1961-03-17.

Dr. Joy is also remembered with the dedication of the asteroid (11769) Alfredjoy.