Weather Talk: Measuring length of full day with high accuracy possible
An atomic second is defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between two hyperfine levels of the ground state of cesium 133 atoms.
Although this detail may not seem relevant to much in our daily life, it actually is more relevant than we might think. Because we can measure time so precisely now, it is possible to measure the length of a full day very accurately. And we know that it is changing because our planet’s rotation is slowing down. One day is about two-thousandths of a second longer than a hundred years ago.
The GPS systems in our phones, cars and running watches rely on light-speed communications from satellites. If the clocks in the satellites are different from our GPS devices by even a millionth of a second, errors approaching half a mile are possible. This is why these systems must be almost constantly recalibrated.
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