Edwin Hubble was a man who changed our view of the Universe. In 1929 he showed that galaxies are moving away from us with a speed proportional to their distance. The explanation is simple, but revolutionary: the Universe is expanding.

Hubble was born in Missouri in Nov. 20 1889 (died at Sept.28, 1953). His family moved to Chicago in 1898, where at High School he was a promising, though not exceptional, pupil. He was more remarkable for his athletic ability, breaking the Illinois State high jump record. At university too he was an accomplished sportsman playing for the University of Chicago basketball team. He won a Rhodes scholarship to Oxford where he studied law. It was only some time after he returned to the US that he decided his future lay in astronomy (he completed his PhD at Chicago's Yerkes Observatory in 1917).

In the early 1920's Hubble played a key role in establishing just what galaxies are. It was known that some spiral nebulae (fuzzy clouds of light on the night sky) contained individual stars, but there was no consensus as to whether these were relatively small collections of stars within our own galaxy, the 'Milky Way' that stretches right across the sky, or whether these could be separate galaxies, or 'island universes', as big as our own galaxy but much further away. Using the theoretical groundwork of Henrietta Swan-Leavitt and Harlow Shapley, in 1924 Hubble measured the distance to the Andromeda nebula, a faint patch of light with about the same apparent diameter as the moon, and showed it was about a hundred thousand times as far away as the nearest stars. It had to be a separate galaxy, comparable in size our own Milky Way but much further away. He composed (1925) the classification scheme for the structure of galaxies that is still in use today

Hubble was able to measure the distances to only a handful of other galaxies, but he realised that as a rough guide he could take their apparent brightness as an indication of their distance. The speed with which a galaxy was moving toward or away from us was relatively easy to measure due to the Doppler shift of their light. Just as a sound of a racing car becomes lower as it speeds away from us, so the light from a galaxy becomes redder. Though our ears can hear the change of pitch of the racing car engine our eyes cannot detect the tiny red-shift of the light, but with a sensitive spectrograph Hubble could determine the redshift of light from distant galaxies.

He determined the extragalactic distance scale by locating Cepheid Variables in the galaxy M31 from the Mount Wilson Observatory in 1924 and NGC 6822 (in Capricornus) in 1925. Using the galactic period-luminosity relationship (which was actually not quite correct, as was discovered by Baade), he determined distances. Extending distance determinations by using the brightest star in galaxies, he (with Milton Humason) proposed the Hubble Law , which states v = Hl. Hubble's original 1936 value for H of 526 km s^-1 Mpc^-1 was reduced to 200 km s^-1 Mpc^-1 after the work of Baade, and to between 50 and 100 km s-1 Mpc-1 when Sandage discovered that some of the "stars" Hubble had identified in distance galaxies were actually H II regions. Hubble gives an account of the discovery of the extragalactic nebulae (galaxies) in Realm of the Nebula (1936).