Doppler Effect Red Shift, Blue Shift

Doppler Effect in light waves emitted from a moving star. Animation shows how the apparent increase in frequency observed in light waves emitted from an approaching star (or conversely a decrease in frequency in light waves emitted from a receding star) happens. This causes a red shift for an observer watching the star recede (left of animation) and a blue shift for an observer watching the star approach (right of animation).