>>12078194Basically when objects move towards or away from us at great speeds, their spectrum changes. When they move towards us the wavelength gets smaller making it appear more blue, and when it moves away, the spectrum gets longer. This is known as the doppler effect. Its the same reason that race cars go 'nnnNNNNYOOOOoooo" as they go by. Its the doppler effect applied to sound.
This helpful when determining how far away celestial bodies are from us. Since the universe is expanding, things that are further away are moving away faster. If we know the emmision spectrum of a star (through study of its lifecyle) we can figure out how far away it is by how redshifted it is.
