Earth's Rotation Sped Up on July 9—and We're Not Sure Exactly Why

Newsweek

10-07-2025

Based on facts, either observed and verified firsthand by the reporter, or reported and verified from knowledgeable sources.
Newsweek AI is in beta. Translations may contain inaccuracies—please refer to the original content.
If you've felt like summer days are flying by, you're not wrong—at least not scientifically. Experts have observed that Earth's rotation is speeding up, making some days slightly shorter than the standard 24 hours.
On July 9, 2025, scientists at the International Earth Rotation and Reference Systems Service (IERS) reported that the Earth completed its rotation approximately 1.3 to 1.6 milliseconds faster than the standard 24-hour period. Moreover, this is expected to happen again on July 22 and August 5 this year.
While the differences in time are imperceptible to humans, it's significant enough to raise eyebrows in the world of ultra-precise timekeeping.
It takes Earth 24 hours, or 86,400 seconds, to make one full rotation around its axis, but Earth's rotation isn't perfectly constant.
It speeds up and slows down due to a complex mix of factors, and scientists monitor these fluctuations using atomic clocks. These clocks are so accurate that they only lose or gain a second every 100 million years.
Why is Earth spinning faster?
"The causes of the recent acceleration are not fully understood," Astrophysicist Graham Jones told Newsweek. There's no single reason why Earth is spinning faster, but scientists point to several likely contributors.
One major factor is the Moon. Earth's natural satellite exerts a powerful gravitational pull that generally slows our rotation over long timescales. But during certain points in the Moon's elliptical and tilted orbit, especially when it's farthest from Earth and at its steepest angle relative to the equator, lunar gravity can have a speeding effect.
On the key dates this summer, the Moon will be near its farthest point and at a sharp orbital tilt—conditions that appear to align with these shorter days.
Another key factor is the constant exchange of angular momentum between different parts of the Earth system. "If the atmosphere speeds up, the solid Earth slows down—and vice versa," geophysicist professor Richard Holme of the University of Liverpool told Newsweek. Over longer periods, similar exchanges occur between Earth's mantle and its fluid core.
A file photo of a globe spinning.
A file photo of a globe spinning.
Stockbyte/Getty Images
Other factors thought to impact the speed of the Earth's spin include geological activity, like earthquakes, which can redistribute the planet's mass and affect its spin, though there are no recent large quakes to link to this year's speed increase.
Glaciers melting as a result of climate change can also shift water masses around the planet, altering Earth's axis, though this is usually expected to slow the planet's rotation rather than speed it up.
"Studies support the idea that the redistribution of ice and water affects Earth's rotation, although this likely doesn't explain the recent acceleration," Jones said.
What are the implications?
It may sound like cosmic trivia, but the consequences of Earth's rotational changes are real.
"If this faster rotation continues, a negative leap second may be required to keep our clocks in sync with the Sun. This would mean a second is skipped—there would be a minute with only 59 seconds," Jones explained.
This would cause problems for global infrastructure like satellite navigation, military systems and global financial markets that rely on split-second precision. A mismatch between the planet's rotation and atomic time could wreak havoc on these networks.
"For navigation, GPS is corrected for position for an offset caused by a cumulative effect of change in rotation rate. For timekeeping systems, there is mention of possibly adopting a negative leap second—an extra (or in this case, one fewer) second in the day to make sure we line up again," Holme said.
To date, all adjustments to time have involved adding a leap second. But if Earth's current acceleration continues, scientists may soon need to subtract one instead, a move that could pose new challenges for timekeeping systems and software.
Is Earth speeding up?
The shorter days noticed by scientists have sparked interest, but in general, the Earth is slowing in rotation.
"There were 400 days in a year 300 million years ago, for about the same length of year," Holme explained.
"Overall, the Earth's rotation is slowing," Jones agreed. "But within this overall pattern, there are ups and downs in Earth's rotational speed."
Do you have a tip on a science story that Newsweek should be covering? Do you have a question about Earth's rotation? Let us know via [e-mail].