A light wave has mass 0, so except his movement in one direction with lightspeed C it can't be moved in an other direction. So the crossing is always the same point (don't consider that space itself is also expanding according theory). Consider you can still track the light waves after a while. When the light source was there in that point, and not anymore after a while, the source was/is moving. In theory you could determine if an object is moving or not somewhere in space ?