Propagation of the light-wave is just the same as that of the sound-wave; there exists Doppler Effect. The light source, the medium (“ether”), the observer are the three basic elements for forming Doppler Effect. The relative motion among these three elements is the basic condition for forming Doppler Effect. Among the four basic factors, not a single one can be omitted. If there is lack of the medium (“ether”), Doppler Effect will not appear; and it is unable to explain the reason of forming Doppler Effect. Doppler Effect of light-wave propagation shows that the light-wave propagation needs the medium (“ether”).
Doppler Effect; light source; ether; medium; observer; relative motion; Relativity Theory; Special Theory of Relativity; wave-model; constancy of the light velocity.