1919 - An experiment conducted by Sir Arthur Eddington, an English astronomer, during a solar eclipse proves Einstein's theory that light is bent by gravity.
1924 - U.S. astronomer Edwin Hubble is the first to prove the existence of another galaxy: the Andromeda galaxy.
1927 - George Lemaitre, a Belgian astronomer, along with George Gamow, devises a theory to explain how the universe began as an explosion of incredibly dense matter and energy. In 1947, Fred Hoyle names this the Big Bang theory.
