Harlow Shapley (November 2, 1885 – October 20, 1972) is notable for his groundbreaking 1918 work using Cepheid variables to estimate the size of the Milky Way Galaxy and the sun's position within it as well as in 1953 proposing the "Liquid Water Belt" theory, now known as the concept of a habitable zone.

Martin Ryle (1918-1984) was a British astrophysicist who developed the aperture synthesis technique of interferometry and constructed large radio telescopes, using them to discover and catalogue numerous radio sources. He guided the Cambridge radio astronomy group in the production of several important radio source catalogues.

Harry H. Plaskett FRS (July 5, 1893 - January 26, 1980) was a Canadian astronomer who made significant contributions to the fields of solar physics, astronomical spectroscopy and spectrophotometry. From 1932 to 1960, he served as the Savilian Professor of Astronomy at the University of Oxford, and in 1963 was awarded the Gold Medal of the Royal Astronomical Society.

Bertil Lindblad (Örebro, 26 November 1895 – Saltsjöbaden (outside Stockholm, 25 June 1965) was a Swedish astronomer.

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.

Ejnar Hertzsprung (8 October 1873 – 21 October 1967) was a Danish chemist and astronomer.

Hertzsprung was born in Copenhagen. In the period 1911–1913, together with Henry Norris Russell, he developed the Hertzsprung–Russell diagram.