An orbit is one trip in space around Earth. GPS satellites each take 12 hours to orbit Earth. Each satellite is equipped with an atomic clock so accurate that it keeps time to within three nanoseconds—that’s 0.000000003, or three-billionths of a second—to let it broadcast signals that are synchronized with those from other satellites.The signal travels to the ground at the speed of light. Even at this speed, the signal takes a measurable amount of time to reach the receiver. The difference between the time when the signal is received and the time when it was
sent, multiplied by the speed of light, enables the receiver to calculate the distance to the satellite. To calculate its precise latitude, longitude, and altitude, the receiver measures the distance to four separate GPS satellites.
