Book 3, Question 89
Why Does GPS Know Where You Are?
Radio beeps take time to travel. So the farther a satellite is, the later its beep arrives. Comparing those delays pins you on the map!
From the book
Page from A Million Whys Book 3
More fun facts
- GPS stands for Global Positioning System.
- GPS uses more than 30 navigation satellites circling Earth.
- GPS satellites orbit about 11,000 miles above Earth and send out radio signals.
- Each GPS satellite has a very precise clock, accurate to within 40 billionths of a second.
- Your phone's GPS receiver compares the time signals from the satellites with its own clock to work out how far away each one is.
- Once it knows its distance from four or more satellites, the receiver can figure out where you are.
- People once used the stars to find their way. GPS uses satellites instead.
Sources: NASA Space Place, NIST, NOAA Ocean Service, NOAA
Questions kids ask
How many satellites does GPS need?
A GPS receiver needs signals from at least four satellites to work out where you are.