How does a GPS know exactly where you are on Earth?
Satellite Time-Choir
How does a GPS know exactly where you are on Earth?
You're standing in the middle of a strange city, holding your phone, and a little blue dot announces with total confidence: you are HERE. How does that dot know? You never told it anything. The secret isn't magic — it's a tiny choir of satellites, all singing the same odd little song.
Way up above you — about 20,000 kilometers up — there are dozens of satellites circling the Earth. They don't beam a picture of you down. They don't even know you exist. Each one just keeps shouting the same simple message, over and over, in every direction: "It is exactly this time, and I am satellite number so-and-so."
