Edwin Hubble (1889-1953) was an American astronomer. With his telescope, Hubble demonstrated the existence of other galaxies other than our own, the Milky Way, and in so doing profoundly changed our understanding of the universe. He showed the immensity of the universe, now calculated to be over thirteen billion light years across.
Hubble showed that the universe is expanding. Finally, he showed that light coming from other galaxies, redshift, increased in proportion to the distance of that galaxy from the Milky Way.
Hubble’s discoveries consist of the fact that there is more than one galaxy. During his time, early part of the twentieth century, astronomers believed that there was only one galaxy. Hubble’s observations in 1923 conclusively showed the existence of many galaxies, now believed to be in the billions. His observations showed that the Friedman-Lamaitre contention that the universe is expanding is correct.
Hubble’s later career was devoted to having astronomy considered a part of physics; apparently, he wanted astronomers to be considered worthy of the Nobel Prize in physics, since there was no independent category for astronomy. His wishes were granted and today astronomers are considered along with physicists in awarding the Nobel Prize for physics.
Edwin Hubble. The Realm of the Nebulae. (1936)
Edwin Hubble. The Observational Approach to Cosmology. (1937)