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The rotation has changed ever so slightly.

You won’t notice it, but the day just got a tiny bit shorter because of Friday’s giant earthquake off the coast of Japan.

NASA geophysicist Richard Gross calculated that Earth’s rotation sped up by 1.8 microseconds. That’s because of the shift in Earth’s mass caused by the 8.9-magnitude earthquake. A microsecond is one-millionth of a second.

Friday’s change in rotation speed is slightly more than the one caused by last year’s larger Chile earthquake. But 2004’s bigger Sumatra earthquake caused a 6.8-microsecond shortening of the day.

Changing the length of a day by that much may sound like an impressive feat, but in fact that magnitude of change is so small that it’s lost over time. Seasonal changes in ocean currents and the atmosphere move the length of a day back and forth over a range of 1 millisecond, or 1,000 microseconds.

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