The Doppler effect was named after Christian Johann Doppler. This Austrian physicist observed and explained the changes in pitch and frequency of sound and light waves, as well as all other types of waves, caused by the motion of moving bodies. The general rule of the Doppler effect is that the wave frequencies of moving bodies rise as they travel toward an observer and fall as they recede from the point of observation.

While Doppler, in 1842, demonstrated the phenomenon named after him in the area of sound waves, in the same year he also predicted that light waves could be shown to exhibit the same response to the movement of bodies similar to those of sound waves.

The response of sound waves to moving bodies is illustrated in the example of the sounding of the locomotive whistle of a moving train. When the train blows its...