How does GPS work?
The GPS satellites continuously transmit an estimate of their position, digital codes, and a precise time signal. A GPS receiver uses an internal clock and the codes to determine the distances to at least four satellites. Distance is calculated by multiplying the time it takes the radio signals to reach the receiver times the speed at which the signals travel, approximately 186,000 miles/second, which is the speed of light. Knowing where the satellites are located when they transmit their signals, the receiver can calculate its position on Earth or in the air.