Grade 9 · Science
How GPS Knows Where You Are
When a phone shows a blue dot on a map, it can seem as if the phone simply knows where it is. In fact, the phone is solving a puzzle, and the clues are falling from space. About thirty satellites that belong to the Global Positioning System, or GPS, circle Earth roughly 20,000 kilometers (about 12,500 miles) up, and each one makes a full orbit about twice a day. Their paths are planned so that, from almost anywhere on the planet, several are always above the horizon.
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