Every six years, Earth spins slightly faster and then slower

Cyclic changes in day length overlie decades-long trends

4:14pm, July 10, 2013

The world turns slightly faster and slower on a regular 5.9-year cycle, a new study suggests. Researchers also found small speed changes that happen at the same time as sudden alterations in Earth’s magnetic field.

The world’s rotation speed can change slightly, by up to milliseconds per day, because of shifts in winds or the movement of fluid in Earth’s interior. Scientists can measure how fast the Earth spins by observing distant objects in space and timing how long they take to come back into view — that is one day length.

The new study, published in the July 11 Nature, found trends in day length after subtracting the effect of weather, allowing researchers to home in on the effect of Earth’s fluid core.

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