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Earth’s Rotation Breaks Records with Successive Millisecond-Short Days

Atomic-clock data confirm July 9 and 10 as the shortest days of 2025, forecasting July 22 to shave another 1.34 ms from a solar day.

Image
This stack composite photo shows a paddy rice field under the starry sky in Shuangyashan City, northeast China's Heilongjiang Province, May 25, 2025. With paddy rice transplanting largely concluded in Heilongjiang, the vast black soil in the province is now dressed in green, hinting the hope for a bountiful harvest. The Milky Way spreading across a starry sky is mirrored in waterlogged paddy rice fields, making a breathtaking scene in the early summer night. (Photo by Qu Yubao/Xinhua via Getty Images)
An atomic clock in the time laboratory of the Physikalisch-Technische Bundesanstalt (PTB) in Germany. These devices use lasers and atoms to calculate time with extreme precision.
A view of Shoesmith Glacier on Horseshoe Island in Antarctica. Melting ice here and in Greenland is affecting Earth's rotation speed.

Overview

  • Measurements from IERS and global atomic clocks show July 9 was 1.30 ms and July 10 was 1.36 ms shorter than a standard 24-hour day.
  • Forecasts indicate July 22 will set a new brief-day record at 1.34 ms below the usual rotation period.
  • The International Earth Rotation and Reference Systems Service has ruled out adding a leap second in 2025 and is preparing protocols for a potential negative leap second by 2029.
  • NASA researchers suggest Earth may have hit the Moon’s gravitational 'sweet spot,' providing a temporary boost to rotational speed.
  • Ongoing studies are examining core dynamics, atmospheric shifts, glacial melt and seismic events as contributors to the spin-up, with implications for GPS accuracy and global timekeeping.