Astronomer Edwin Hubble discovered the Andromeda galaxy, according to the Space Telescope Science Institute. Hubble discovered the galaxy in 1923, after studying the Andromeda nebula. This also settled the debate among astronomers regarding the contents of nebulae.
Hubble photographed the Andromeda nebula from his telescope in California. Though science at the time did not fully understand nebulae, Hubble calculated the distance between the Earth and the stars as well as the components in the nebula. Though some scientists believed the nebula was filled with gas, Hubble discovered it was actually a galaxy filled with stars. Beyond the Andromeda galaxy, Hubble noted other possible galaxies. This transformed the idea of the universe and the way in which astronomers viewed nebulae. Future work by modern astronomers determined there were over 100 billion different galaxies within the universe.