Earth is spinning faster, leading timekeepers to consider an unprecedented move

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Earth is spinning faster, leading timekeepers to consider an unprecedented move

By Jacopo Prisco, CNN
7 min read
Updated 7:01 PM EDT, Mon July 21, 2025


Earth is spinning faster this summer, leading astronomers to notice that some days have clocked in at slightly less than the standard 24 hours. This stack composite photo shows a paddy rice field under the starry sky in Shuangyashan City, in northeast China's Heilongjiang Province. Qu Yubao/Xinhua News Agency/Getty Images

(CNN) — Earth is spinning faster this summer, making the days marginally shorter and attracting the attention of scientists and timekeepers.

July 10 was the shortest day of the year so far, lasting 1.36 milliseconds less than 24 hours, according to data from the International Earth Rotation and Reference Systems Service and the US Naval Observatory, compiled by timeanddate.com. More exceptionally short days are coming on July 22 and August 5, currently predicted to be 1.34 and 1.25 milliseconds shorter than 24 hours, respectively.

The length of a day is the time it takes for the planet to complete one full rotation on its axis —24 hours or 86,400 seconds on average. But in reality, each rotation is slightly irregular due to a variety of factors, such as the gravitational pull of the moon, seasonal changes in the atmosphere and the influence of Earth’s liquid core. As a result, a full rotation usually takes slightly less or slightly more than 86,400 seconds — a discrepancy of just milliseconds that doesn’t have any obvious effect on everyday life.

However these discrepancies can, in the long run, affect computers, satellites and telecommunications, which is why even the smallest time deviations are tracked using atomic clocks, which were introduced in 1955. Some experts believe this could lead to a scenario similar to the Y2K problem, which threatened to bring modern civilization to a halt.

Atomic clocks count the oscillations of atoms held in a vacuum chamber within the clock itself to calculate 24 hours to the utmost degree of precision. We call the resulting time UTC, or Coordinated Universal Time, which is based on around 450 atomic clocks and is the global standard for timekeeping, as well as the time to which all our phones and computers are set.

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