One piece of evidence that proves that the speed of light is indeed constant comes from the observation
A) that the light from the stars in a binary system is smeared out by their mutual motion
B) that the light from the stars in binary system is Doppler shifted by their mutual motion
C) of gravitational waves emitted from binary systems
D) that stars in a binary system appear as distinct points of light

Question

Quizplus · Accepted Answer

If the speed of light were not constant, then the light from the stars in a binary system would appear to move with different speeds when the stars are moving towards or away from us, causing them to blur and no longer appear as distinct points of light. The fact that they still appear as distinct points of light suggests that the speed of light is constant.

One Piece of Evidence That Proves That the Speed of Light