We all are familiar with the Doppler Effect. It is why when an emergency vehicle has the sirens on the pitch of the sirens drops as the vehicle passes you. (The difference in speed between you and the emergency vehicle either compress or elongates the sound waves from the siren which changes the pitch of what you hear.) Hubble space telescope was used to identify other galaxies and thanks you certain types of stars that burn with a known standard brightness. NASA scientists were then able to detect shifts in the standard color of the light to know what direction the other galaxies were moving in relation to us. This means that the Doppler Effect works with light waves too! (And now the science gets crazy) The light from a galaxy moving away from us shifts to the red and a galaxy moving towards would shift to the violet. Just with sound the faster the speed towards or away from us the more the light would shift either towards red or violet. The c...