Edwin Powell Hubble (1889 - 1953)
Edwin was an American astronomer, inspired by the science fiction books he read as a child. He graduated from Oxford University with a degree in law philosophy, before returning to university (this time the University of Chicago) to study astronomy. Not long later, he was recruited by California's Mount Wilson Observatory to aid in the construction of their new telescope. However, before accepting the job, he completed a doctorate in astronomy, enlisted in the US Army, and served a tour of duty in World War I.
Whilst working at Mount Wilson, Edwin used the observatory's telescope to prove that other galaxies existed outside of the Milky Way. To do this, he compared the various degrees of luminosity among Cepheid variable stars. He was able to estimate that the Andromeda 'nebula' was nearly 900,000 lightyears away from the Milky Way, and therefore it must be its own galaxy. Renamed the Andromeda galaxy, it was later shown to be much more distant, at nearly 2.48 million lightyears away.
In the early 1920s, Edwin began to study the spectral lines of galaxies, and in particular their spectral shifts. Working alongside the astronomer Milton Humason, they published their work together in 1929. The work theorised that the redshift of the emission from a galaxy (which showed that all galaxies are moving away from one another, and the Universe is expanding) is directly related to the distance of the galaxy from Earth. Put another way, the recessional velocity of a galaxy increases with its distance from Earth. This simple relation became known as Hubble's Law.
NASA named the Hubble Space Telescope in Edwin's honour.