How does that work? The satellites stay in known positions and the signals travel at the speed of light. Each signal includes information about the satellite it came from and a time-stamp that says when it left the satellite. Since the signals are radio waves, they must travel at the speed of light. By nothing when each signal arrives, the receiver can figure out how long it took to travel and how far it has come—in other words, how far it is from the sending satellite. With three or four signals, the receiver can figure out exactly where it is on Earth.