How GPS Finds Your Car: Four Satellites and a Clock
How many satellites does your car need to find itself? Usually four, and the reason is a clock: the one in your car is a little off, so the receiver works out how far off it is while it works out where it is. This episode follows the signal down from orbit: why a billionth of a second is a school ruler of light, why the satellites' own atomic clocks would run fast if nobody allowed for it, why the blue dot still wanders downtown, and the clock nobody sees: how the same signal helps cell towers, the power grid and traders agree on the time, alongside their other clocks.
What this episode is…
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