Explained Simply #3: How does GPS know where you are?
Your phone times signals from 4+ satellites; distance = time × light speed, and the satellite clocks are corrected for relativity (about 38 microseconds a day).
How does your phone know EXACTLY where you are? 📍🛰️
1️⃣ TIME SIGNALS: GPS satellites about 20,000 km up keep sending the exact time. Your phone times how long each signal takes to arrive — about 0.07 seconds.
2️⃣ DISTANCE: time × light speed = distance (0.07 s × 300,000 km/s ≈ 20,000 km). One distance puts you on a big sphere, three distances pin you to one spot — and a fourth satellite fixes your phone's own clock.
3️⃣ CLOCKS MATTER: 1 microsecond off = 300 m wrong! So every satellite carries atomic clocks — they even correct for Einstein's relativity (about 38 microseconds a day).
Time, distance, you!
Read the voiceover (transcript)
- How does GPS know where you are?
- Satellites keep sending the time. Your phone times each signal.
- Time times light speed gives distance. Three pin you down. A fourth fixes the clock.
- A millionth of a second off? Three hundred metres wrong! So satellites carry atomic clocks.
- Time, distance, you!
- Next: how Wi-Fi sends a video! Follow for more!
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