Why Sunday May Now Be The Shortest Day Of The Year As Earth Slows Down

Topline

Earth’s recent spell of unusually rapid rotation may have peaked, with the shortest day of 2026 set to occur on Sunday, July 26 — though people will not notice any difference. New data from the International Earth Rotation and Reference Systems Service — the keeper of global time — reported by TimeAndDate.com indicates the planet’s rotation is slowing again after several years of record-breaking short days.

The latest mid-July predictions from IERS suggest the shortest day of 2026 will occur on Sunday, July 26, when Earth’s day is expected to measure around 0.65 milliseconds shorter than the standard 24 hours.

getty

Key Facts

Time on Earth is based on Coordinated Universal Time, which closely follows the planet’s rotation. As Earth’s rate of rotation changes, “leap seconds” are added or taken away every so often. So far, leap seconds have only ever been added, with a slight slowing of Earth’s rotation observed by atomic clocks.

Earth takes 86,400 seconds to complete one rotation (a 24-hour day). The shortest day, recorded July 10, 2025, was -1.37 milliseconds below that.

While still technically a shorter-than-average day, it represents a noticeable change compared with 2025, although the difference is only about seven-tenths of a millisecond.

The new data comes in the wake of a report in June stating that Earth’s rotation is gradually slowing as climate change melts glaciers and polar ice sheets.

Earth’s Fastest Spin May Be Over

Earth’s recent acceleration surprised scientists after decades of expectations that the planet’s rotation would continue its gradual long-term slowdown, according to Graham Jones, an astronomer at TimeAndDate.com. The trend first became apparent in 2020, when Earth recorded the 28 shortest days of the atomic clock era. New records followed in 2022, while 2025 produced another run of exceptionally short days. That raised the possibility of the world’s first negative leap second and slightly altered the path of a solar eclipse, causing some cities in Texas to be excluded. Tiny differences in Earth’s rotation affect how precisely eclipse paths are calculated. However, the latest figures suggest the period of faster rotation may now have peaked.

Earth takes 86,400 seconds to complete one rotation (a day). The shortest day, recorded in 2025, was -1.37 milliseconds below that. Image shows a startrail, a composite showing how the night sky revolves around Polaris, the North Star, which Earth's northern axis points at. Taken at a prayer pagoda in Inner Mongolia.

getty

Why Earth’s Rotation Changes

Earth’s rotation is constantly changing by tiny amounts, even though the planet remains an exceptionally reliable timekeeper. “Earth’s spin is affected by the moon’s monthly orbit,” writes Jones. “We spin more slowly when the moon is above the equator, and more quickly when the moon is to the north or south of the equator.” Meanwhile, tidal forces gradually slow the planet over centuries and millennia. However, other factors remain more difficult to predict — such as movements within Earth’s liquid core, oceans and atmosphere. “In my opinion, Earth’s rotation has started to decelerate,” Leonid Zotov, a geodesy specialist at Moscow State University, told TimeAndDate.com. “The deepest minimum over the past decade has been passed: Earth has passed its highest velocity.”

Background

Earlier this year, research by the University of Vienna and ETH Zürich concluded that Earth’s rotation is gradually slowing as climate change melts glaciers and polar ice sheets, redistributing water across the planet and subtly lengthening the day. Only 48% of Americans believe climate change is the result of human activity.