Hubble's Law

Discovered by: Edwin Hubble, Alexander Friedmann and Georges Lemaître.

What is it? This Doppler shift-measured velocity of various galaxies receding from the Earth is approximately proportional to their distance from the Earth for galaxies up to a few hundred megaparsecs away.

Why is it important? Hubble's law is considered the first observational basis for the expansion of the universe and today serves as one of the pieces of evidence most often cited in support of the Big Bang model.