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Earth Spins Faster on July 22, Marking Second-Shortest Day of 2025

Global timekeepers have ruled out a leap second for 2025 as they draft protocols for a potential negative leap second by 2029

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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.

Overview

  • July 22 is projected to be 1.34 milliseconds shorter than a standard day, making it the second-shortest day of 2025 after July 10’s 1.36 ms shortening
  • Atomic clocks and satellite measurements have captured a trend of record-short days since 2020, with the fastest spin on July 5, 2024 shaving off 1.66 ms
  • The International Earth Rotation and Reference Systems Service has confirmed that no leap second will be added at the end of 2025
  • Researchers are examining lunar declination effects, shifts in the liquid core and mass redistribution from melting ice and changing oceans as possible causes of the acceleration
  • If Earth’s rotation continues to speed up, a negative leap second—subtracting a second from UTC—may be required around 2029 to keep clocks aligned