News 40 Weather Reports: The day the Earth spun a fraction too fast

Did you notice that Wednesday was the shortest day of the year?

BOWLING GREEN, Ky. (WNKY) – Each tick of the clock marks a second in a day, normally 86,400 of them. But on July 9, 2025, Earth completed its rotation 1.3 milliseconds faster than usual, making it at least the shortest day this year if not ever recorded since atomic clocks came online.

Scientists say this abrupt speed-up isn’t a daily occurrence — instead, it aligns with specific astronomical moments, particularly when the Moon reaches certain positions along its tilted and elliptical orbit. As a result, July 22 and Aug. 5 are also projected to be among the shortest days this summer.

“This is a bit unusual, although there have been more recordings of these shorter days happening within the last couple of decades,” said Shane Holinde, director of outreach at the Kentucky Climate Center and the Kentucky Mesonet.

Earth’s rotation historically slows slightly over centuries, adding around 2 milliseconds per century due to tidal forces with the Moon. Yet recent readings have surprised researchers: since 2020, the planet has exhibited occasional bursts of faster spin, including the record-setting run on July 5, 2024, which was around 1.66 milliseconds shorter than the standard day.

The culprit? Experts pinpoint the Moon’s distance from Earth’s equator as the primary cause. When the Moon drifts farther from the equatorial plane, its gravitational estimate on Earth diminishes, allowing the planet’s spin to quicken slightly, similarly to how a figure skater spins faster by pulling in her arms.

“This is not something that trims the amount of hours per day or even the amount of minutes per day. It happens so quickly that… you’re not even going to notice a difference,” Holinde said.

Timekeepers at the International Earth Rotation and Reference Systems Service (IERS) are tracking the trend. If slight days like these continue to accumulate, they may consider a historic adjustment, a negative leap second, which would subtract a second from Coordinated Universal Time (UTC) for the first time.

While Earth’s spin is closely monitored, it doesn’t mean the change is constant. These short-day events correspond to specific orbital alignments and are not happening daily. Each of the summer’s projected short days correlates directly to when the Moon reaches its maximum tilt away from the equator.

Scientists continue to study what might also contribute to these surprising shifts. Some researchers believe that internal changes, such as convective flows in Earth’s molten core or shifts in mass distribution elsewhere, could play a role, although these theories are not yet confirmed.

For now, the missing milliseconds won’t affect your day-to-day life. The Earth remains comfortably in its celestial rhythm, but the clock is ticking in the world of precision timekeeping