quality:corruption
Slipher's observations

In 1912, Vesto M. Slipher measured the first Doppler shift of a " spiral nebula " (the obsolete term for spiral galaxies) and soon discovered that almost all such nebulae were receding from Earth. He did not grasp the cosmological implications of this fact, and indeed at the time it was highly controversial whether or not these nebulae were "island universes" outside the Milky Way galaxy.