What does GPS stand for?

GPS began as a military project, but today billions of people use it every day without thinking about it.

How GPS works

1. GPS satellites orbit about 20,200 km above Earth, each carrying extremely precise atomic clocks.
2. Each satellite constantly broadcasts its position and the exact time.
3. Your device receives signals from at least four satellites.
4. By measuring how long each signal took to arrive, it calculates the distance to each satellite and works out where you are, a method called trilateration.

Your phone only receives signals; it doesn’t send anything to the satellites.

Einstein makes GPS work

GPS clocks must be adjusted for relativity. Because the satellites move fast and experience weaker gravity, their clocks run about 38 microseconds a day faster than clocks on the ground. Without correction, GPS positions would drift by kilometers every day. See what Einstein’s general relativity is.

How GPS was built

1. 1973The US Department of Defense begins the GPS project
2. 1978The first GPS satellite launches
3. 1983After a Korean airliner strays off course and is shot down, the US promises to open GPS to civilian use
4. 1995The system becomes fully operational
5. 2000The US switches off “selective availability,” making civilian GPS much more accurate

Other satellite navigation systems

Together these are called GNSS (Global Navigation Satellite Systems). Most modern phones use several at once for better accuracy.

What GPS is used for

• Maps and driving directions
• Ride-sharing and food delivery
• Aircraft and ship navigation
• Precise timing for banks, phone networks and power grids

For another way to share an exact spot, see what what3words is. Satellites began with Sputnik 1.