Earth is spinning faster this summer, making some days in July and August marginally shorter, according to a recent study.
July 10 was the shortest day of the year so far, lasting 1.36 milliseconds less than 24 hours, while similar 'short days' expected on July 22 and August 5, as per New estimates released by the International Earth Rotation and Reference Systems Service and the US Naval Observatory, compiled by timeanddate.com.
On average, from the point of view of the Sun, Earth completes one full rotation on its axis in exactly 86,400 seconds, which totals to 24 hours.
The shortest length of day, or LOD, ever recorded by atomic clocks, was -1.66 ms on July 5, 2024.
Short-term variations in LOD are affected by the orbit of the Moon. Earth spins quicker when the Moon's position is far to the north or south of Earth's equator.
The Moon will be around its maximum distance from Earth's equator on the three possible dates for the shortest LOD in 2025.
Why has Earth accelerated, and when will it slow down again? These are difficult questions to answer for scientists and timekeepers.
Long-term variations in Earth's spin speed are affected by a long list of factors that includes the complex motion of Earth's core, oceans, and atmosphere.
"Nobody expected this," says Dr. Leonid Zotov, a leading authority on Earth rotation at Moscow State University. "The cause of this acceleration is not explained."
Most scientists believe it is something inside the Earth. Ocean and atmospheric models don't explain this huge acceleration.
Early last year, there were indications that Earth might be slowing down, and Dr. Zotov predicted that Earth would decelerate. "But the future will show if that's right," he cautioned.
That prediction turned out to be premature. Yet Dr. Zotov is striking a similar note in 2025: "I think we have reached the minimum. Sooner or later, Earth will decelerate."
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