Earth completed rotation 1.34 ms faster on July 22, 2025—marking one of the shortest days ever and hinting at a possible negative leap second.
July 22, 2025 – A Remarkable Astronomical Phenomenon Unfolds
In a subtle yet significant cosmic event, Earth completed its full rotation on July 22, 2025, 1.34 milliseconds faster than the standard 24-hour day—making it one of the shortest days ever recorded.
While imperceptible in daily life, this micro-shortening of time marks a notable moment in Earth’s rotational history and raises new questions for scientists monitoring our planet’s dynamic behavior. If this pattern of acceleration continues, experts warn it could lead to an unprecedented adjustment to atomic time—a negative leap second—as early as 2029. Such a change has never been made before in the history of timekeeping.
Understanding Earth’s Changing Rotation
Earth’s rotation has never been completely fixed. In fact, billions of years ago, a day on Earth lasted just 19 hours, shaped by the gravitational tug-of-war between solar atmospheric tides and lunar ocean tides. Over time, the Moon’s tidal friction has gradually slowed Earth’s spin while pushing the Moon farther away. This steady slowdown has generally led to longer days.
But in recent years, that long-term trend appears to have reversed—at least temporarily.
Breaking Records Since 2020
Before 2020, the fastest rotation ever recorded occurred in 2005, with a day that was 1.05 milliseconds shorter than usual. But beginning in 2020, Earth began smashing its own records.
- July 5, 2024 currently holds the record as the shortest day ever measured, at 1.66 milliseconds less than 24 hours.
- July 10, 2025, now appears to be the shortest day of this year so far, clocking in at 1.36 milliseconds early.
- July 22, 2025, is a close runner-up, with a rotation 1.34 milliseconds shorter.
- August 5, 2025, is forecasted to be around 1.25 milliseconds shorter, potentially making it the third-shortest day this year.
Why Is Earth Spinning Faster?
The underlying cause of this mysterious acceleration is still unknown, sparking intense debate within the scientific community. Some theories include:
- Melting polar ice and rising sea levels, which redistribute Earth’s mass. However, recent studies suggest this may be moderating rather than causing the acceleration.
- A slowing of Earth’s liquid core, which could be redistributing angular momentum in a way that speeds up the mantle and crust.
“Most scientists believe the answer lies deep within Earth,” explains Leonid Zotov, a renowned Earth rotation researcher at Moscow State University. “Ocean and atmospheric models don’t explain this huge acceleration.”
Zotov believes the current speed-up could be a short-term fluctuation and expects Earth’s rotation may decelerate again soon.
What’s Next for Timekeeping?
If the acceleration continues, the global timekeeping community may have to make a dramatic adjustment: subtracting a second from atomic time—a negative leap second—around 2029. This would be a first in human history, as previous adjustments have only ever added time.
For now, scientists continue to monitor Earth’s ever-changing rhythm, trying to understand the forces shaping the heartbeat of our planet.
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