Is Earth's rotation speeding up? Why these 3 summer days may be shorter than usual

Yahoo

11-07-2025

Earth spun just a bit faster than usual on July 9 and is expected to do so again on July 22 and Aug. 5, according to the website TimeAndDate.
Over a millisecond was reportedly shaved off the clock on Wednesday, but the shortest day out of all three predicted will be in August.
This shortening is due to the moon's position relative to Earth and its influence on the planet's rotation.
Here's what to know about why Earth's rotation is speeding up, and how it is shortening three days this summer.
Earth takes 24 hours to complete a full rotation in a standard day, equal to exactly 86,400 seconds.
If a standard day is shortened or lengthened by a number of milliseconds, that added or detracted time is referred to as "length of day," according to the website TimeAndDate.
Until 2020, the shortest "length of day" ever recorded by atomic clocks was -1.05 ms, meaning that Earth completed one daily rotation in 1.05 milliseconds less than 86,400 seconds.
"Since then, however, Earth has managed to shatter this old record every year by around half a millisecond," astrophysicist Graham Jones wrote for TimeAndDate.
That culminated on July 5, 2023, with the shortest day of all time, with a "length of day" of -1.66 ms, according to Jones.
While the variations are expected, recent research suggests that human activity is also contributing to Earth's changing rotation. Researchers at NASA calculated that dwindling ice and groundwater and rising seas have actually increased the length of our days since 2000 by 1.33 milliseconds per century.
Scientists have anticipated that Earth's rotation will quicken enough to create three shorter days between July and August.
The first was Wednesday, July 9, which had about a -1.30 ms "length of day," according to TimeAndDate.
The next two shortened days, though, will be even more truncated. Scientists predicted a -1.38 ms "length of day" July 22, and a -1.51 ms "length of day" Aug. 5.
On these days, the moon will be at its furthest from the Earth's equator, changing its gravitational pull and causing our planet to spin just a tiny bit faster on its axis, according to science news website LiveScience.
Of course, you're unlikely to notice such a minuscule difference in your standard 24-hour day.
But scientists who track and operate atomic clocks may be facing a bit of a predicament.
First introduced in the 1950s, atomic clocks replaced how scientists previously measured the length of a day by tracking the Earth's rotation and the position of the sun. The clocks are also capable of measuring in billionths of a second, or nanoseconds, which are synchronized globally to Coordinated Universal Time (UTC.)
If the clocks are thrown off even a tiny amount, it could also throw off computers, servers, GPS signals, and other networks that rely on accurate times, David Gozzard, an experimental physicist at the University of Western Australia, told the Guardian.
This article originally appeared on The Providence Journal: Earth's rotation speed: These 3 summer days may be shorter than usual