Sound Waves, Light Waves and an Observer (summary) (中山)
Sound waves propagate through air, and light waves propagate through aether. Medium is uniformly isotropic, and speed of waves with respect to medium is constant. So, when a point-like wave source is stationary in medium, waves drawn on a plane are concentric circles. Therefore, if an observer is moving with respect to medium, speed of sound waves and light waves for the observer is not constant.
Note: Light waves using air as a medium propagate in the same way as sound waves.
