How Your Phone Knows Where You Are: GPS in 5 Minutes

Sample post: replace it with your own.

Your phone finds your location to within a few meters, using signals from satellites more than 20,000 km above you. Here’s how.

Satellites that tell the time

Each GPS satellite carries an atomic clock and constantly broadcasts: “I’m here, and the time is now this.”

Distance from time

The signal travels at the speed of light. Your phone checks how long it took to arrive and works out how far away the satellite is.

Four satellites, one answer

• One satellite puts you somewhere on a giant sphere
• Two narrow it to a circle
• Three narrow it to two points
• A fourth fixes your phone’s clock error and picks the right point

Where Einstein comes in

The satellites move fast and sit in weaker gravity, so their clocks run at a slightly different speed than ours. Without correcting for relativity, GPS would drift by kilometers every day.