EDWIN HUBBLE

USA (1889 - 1953)

Edwin Powell Hubble profoundly changed astronomers' understanding of the nature of the universe by demonstrating the existence of other galaxies besides the Milky Way. He also discovered that the degree of redshift observed in light coming from a galaxy increased in proportion to the distance of that galaxy from the Milky Way. This became known as Hubble's law, and would help establish that the universe is expanding.

Source: http://www.pbs.org/soptv/400years/en/