One-Way Speed of Light Relative to a Moving Observer

The one-way speed of light relative to a moving observer is determined using the range equation of the Global Positioning System. This equation has been rigorously tested and verified in the Earth-Centred Inertial frame where light signals propagate in straight lines at constant speed c. The result is a simple demonstration of light speed anisotropy that is consistent with light speed anisotropy detected in other experiments and inconsistent with the principle of light speed constancy. This light speed anisotropy was not observed before because there has been no direct one-way measurement of light speed relative to a moving observer.