Main Question or Discussion Point
I've read that the GPS system has to take into account the Sagnac effect when sending signals from the satellites to the Earth. For those of us who are unfamiliar with the Sagnac effect, it is the delay in receiving(or shorter time in receiving) the signal due to the rotation of the Earth while the signal is in transit to the Earth. Now if the speed of light were always constant then this shouldn't be necessary because the amount of time to receive the signal would only depend on the distance at the time of emission. So what is the official explanation why this doesn't indicate that light is traveling at c+v or c-v relative to us?