[ScottBurson]

Yes, this is the correct answer. It's a relativistic effect that is nonetheless observable at velocities not usually considered to be relativistic.

I think this is extremely cool, BTW: any ordinary refrigerator magnet serves to demonstrate the truth of special relativity. Indeed, since the propagation of a photon involves oscillating electric and magnetic fields, the very existence of light itself depends on relativity.

So in a strange and unexpected way, one could say that when Michelson and Morley went searching for the ether, they actually found it. The fact that the speed of light is the same in every inertial reference frame is precisely what allows it to propagate at all.