Is Earth’s rotation speeding up? Why this July day may be shortest so far in 2025

Does it feel like there's not enough time in the day for everything? Well, that could be because some upcoming days are actually getting shorter.

In fact, today might just be the shortest day you'll ever experience. Ok, maybe it won't be short enough for anyone to actually notice, but every millisecond counts, right? 

As much as a millisecond or more could be shaved off the clock on Wednesday, July 9, on account of how the moon's position relative to Earth is influencing our planet's rotation.

Here's what to know about why Earth's rotation is speeding up, and how it will shorten three days this summer.

Is Earth's rotation speeding up?

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 has actually increased the length of our days since 2000 by 1.33 milliseconds per century.

Will the Earth spin faster July 9? Is July 9 the shortest day?

Scientists anticipate that Earth's rotation will quicken enough to create three shorter days between July and August.

The first is Wednesday, July 9, which will have a predicted -1.30 ms "length of day," according to TimeAndDate.

The next two shortened days, though, will be 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.

Will the sped-up day be noticeable?

Of course, you're unlikely to notice such a miniscule 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 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 physicis at the University of Western Australia, told the Guardian.