When distant galaxies are moving away from us, the very, very, fast light waves they give off are stretched out behind them — since each bit of the light wave is being sent from a little bit further away.
When the light waves from distant galaxies are stretched out in this way, they look redder. This is called red shift.
Red shift was first described by Czech mathematician Christian Doppler in 1842.
Edwin Hubble showed that a galaxy’s red shift is proportional to its distance. So the further away a galaxy is, the greater its red shift — and the faster it must be zooming away from us. This is Hubble’s Law.
The increase of red shift with distance proved that the Universe is growing bigger.
Only nearby galaxies show no red shift at all.
The record red shift is 4.25, from the quasar 8C 1435 + 63. It is 96% of the speed of light.
Red shift can be caused by the expansion of the Universe, gravity or the effect of relativity (see Einstein).
Black holes may create large red shifts.
Red Shift occurs as distant galaxies red shifts so big that they must be moving move away from us. The further away a away from us at speeds approaching the speed of light!