01/01/1925 Edwin Hubble finds that there are other galaxies in the universe
Edwin Hubble, the Expanding Universe, Hubble's Law. Astronomers of the 20th Century.
Hubble's Revolution | How the Universe Works
Life Of Hubble
Edwin Powell Hubble, an American astronomer, provided evidence that the recessional velocity of a galaxy increases with its distance from the earth. He also discovered that many objects previously thought to be clouds of dust and gas and classified as "nebulae" were actually galaxies beyond the Milky Way.