Special Relativity

Doppler with Waves


In the previous section the Doppler Effect was illustrated for photons emitted out the front and back of a spacecraft. Now let us consider a continuous wave depiction of light. The animation will illustrate the Doppler Effect in all directions about the light bulb.


In the animation each wave crest is depicted as an expanding circle.

While watching the animation be mindful of the following.

  • The centre of each circle is the location of where it was emitted. The centres do not move.
  • As the spacecraft moves each centre is progressively right of the previous centre.
  • Each circle expands at c, irrespective of how fast the spacecraft is moving
  • The rate of emission of the wave crests decreases as the speed increases due to time dilation.