The Global Positioning System (GPS) is a space-based satellite navigation system that provides location and time information in all weather conditions, anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites.
In addition to GPS, other systems are in use or under development. The Russian Global Navigation Satellite System (GLONASS) was developed contemporaneously with GPS, but suffered from incomplete coverage of the globe until the mid-2000s.
There are also the planned European Union Galileo positioning system, China’s BeiDou Navigation Satellite System, the Japanese Quasi-Zenith Satellite System, and India’s Indian Regional Navigation Satellite System.
GPS location apps on a smartphone can be very handy when mapping a travel route or finding nearby events. But how does your smartphone know where you are?
Wilton L. Virgo explains how the answer lies 19,312 km over your head, in an orbiting satellite that keeps time to the beat of an atomic clock powered by quantum mechanics.