The two keys to Edwin Hubble's breakthrough discovery were forged by others in the 1910s. The first key, the period-luminosity scale discovered by Henrietta Leavitt, allowed astronomers to ...

Edwin Hubble, a renowned astronomer, revolutionized our understanding of the universe. He proved the existence of galaxies beyond the Milky Way and discovered that the universe is expanding.

Photo: Andromeda nebula plate with Hubble's handwritten circle around the variable star he discovered In 1919 American astronomer Edwin Hubble began work at the Mount Wilson Observatory in ...