He proved that galaxies, composed of stars and planets, exist beyond our own Milky Way. He also proved that they are distributed almost uniformly in every direction.
As Hubble continued his study, he discovered that the universe is expanding. The more distant a galaxy is from Earth, the more its light is shifted toward the red end of the spectrum -- redshifted. In 1929 he determined that the more distant the galaxy from Earth, the greater its redshift, and the faster it appears to move away. Known as Hubble's Law, this discovery is the foundation of the Big Bang theory. The theory states that the universe began after a cataclysmic event in which it underwent a rapid period of inflation. The movement of the galaxies away from us is the continuation of that motion. Hubble's discovery is considered one of the greatest triumphs of 20th century astronomy. However, confirmation was difficult, until the launch of the HST.
With the telescope in orbit, astronomers are getting a picture of the universe clearer than anything they could previously obtain.
