Something thats been bugging me, but unable to find an answer for.. The speed of light (in a vacuum) is absolute, well not really, its relative to the space/time its in. ie. The distant galaxies are moving away from us, but their local light speed is relative to their space/time. So since the earth is moving through space (around the Sun, around the galaxy etc), does light on earth appear to travel faster in one direction than the other? Has anyone made a device for measuring the speed of light in different directions, as to show how much faster, and which direction? and how would it read as the device is taken across and out of solar system? Wouldnt it be useful for measuring spacetime.