The apparent shift in frequency of energy due to the relative motion of the object and the observer?

Is called what?
The Hubble effect
Dopler effect
expanision constant
contraction constant

The Doppler shift is what you hear when a passing siren or train whistle changes frequency as it moves toward you or away from you. It's also the principle behind the radar used by police to measure your speed by the rate of change in frequency of the radar waves returned from your vehicle. When viewing light sources that are moving at a high rate of speed and at a great distance, it makes their colors change.