The Doppler Effect for light is exactly the same because it is for sound. Hubble discovered that things further away from us were moving away from us faster than things close to us. In fact, there is almost a linear relationship among distance and recessional velocity (Hubble’s Law). Astronomers now use the recessional velocity as a gauge of the distance an object is from us. If the speed of light is 3x10^8 m/sec, how fast must something be moving away from us to have us observe a wavelength that is 20% greater than that emitted?