A millionth of a second = 300 m

A millionth of a second = 300 m

Nobody measures the distance to a satellite with a tape measure. You take the time the broadcast took and multiply it by the speed of radio waves. So if the clock is wrong, the distance is wrong too. In a millionth of a second, radio waves travel about 300 m. A clock off by just a millionth of a second shifts the red sphere’s surface by 300 m.

Why?A blink takes about a tenth of a second. A millionth of a second is a hundred thousand times shorter than that. You could never feel it, but light covers 300 m in that time. That’s why GPS only works with extremely accurate clocks.

Learn moreA millionth of a second is called a “microsecond,” written “1 μs.” GPS satellites carry atomic clocks so accurate they would drift only about a second in hundreds of thousands of years. This view zooms way in on a few kilometers around the car. Up this close, even the surface of a sphere more than 20,000 km across looks almost like a flat board.

If a clock is off by a millionth of a second

300 m

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