Harlow Shapley
Harlow Shapley (November 2, 1885 – October 20, 1972) was an American scientist, head of the Harvard College Observatory (1921–1952), and political activist during the latter New Deal and Fair Deal.Shapley used Cepheid variable stars to estimate the size of the Milky Way Galaxy and the Sun's position within it by using parallax. In 1953 he proposed his "liquid water belt" theory, now known as the concept of a habitable zone.
Source: Wikipedia