It is very interesting to read about Hubble's galaxy observation using the red shift/blue shift phenomenon
When objects are moving away, the light emitted experiences a red shift indicating movement away from the observer. Vice versa for the blue shift. Hubble observed this for galaxies etc and made even Einstein scratch his head since his theories up to this point assumed a stagnant space of stars!
Look up Hubble/Red Shift etc on the internet....it is very interesting reading!.
