Faster spinning Earth prompts timekeepers to consider unprecedented move

United News of India

23-07-2025

California, July 23 (UNI) As the Earth is spinning faster this summer, the days have become marginally shorter, 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 five, currently predicted to be 1.34 and 1.25 milliseconds shorter than 24 hours, respectively, reported CNN.
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.
Astronomers also keep track of Earth's rotation — using satellites that check the position of the planet relative to fixed stars, for example — and can detect minute differences between the atomic clocks' time and the amount of time it actually takes Earth to complete a full rotation.
Last year, on July five, 2024, Earth experienced the shortest day ever recorded since the advent of the atomic clock 65 years ago, at 1.66 milliseconds less than 24 hours.
'We've been on a trend toward slightly faster days since 1972,' said Duncan Agnew, a professor emeritus of geophysics at the Scripps Institution of Oceanography and a research geophysicist at the University of California, San Diego.
Since 1972, a total of 27 leap seconds have been added to the UTC, but the rate of addition has increasingly slowed, due to Earth speeding up; nine leap seconds were added throughout the 1970s while no new leap seconds have been added since 2016.
In 1972, after decades of rotating relatively slowly, Earth's spin had accumulated such a delay relative to atomic time that the International Earth Rotation and Reference Systems Service mandated the addition of a 'leap second' to the UTC. This is similar to the leap year, which adds an extra day to February every four years to account for the discrepancy between the Gregorian calendar and the time it takes for Earth to complete one orbit around the sun.
The shortest-term changes in Earth's rotation, Agnew said, come from the moon and the tides, which make it spin slower when the satellite is over the equator and faster when it's at higher or lower altitudes. This effect compounds with the fact that during the summer Earth naturally spins faster — the result of the atmosphere itself slowing down due to seasonal changes, such as the jet stream moving north or south; the laws of physics dictate that the overall angular momentum of Earth and its atmosphere must remain constant, so the rotation speed lost by the atmosphere is picked up by the planet itself.
Similarly, for the past 50 years, Earth's liquid core has also been slowing down, with the solid Earth around it speeding up.
By looking at the combination of these effects, scientists can predict if an upcoming day could be particularly short.
'These fluctuations have short-period correlations, which means that if Earth is speeding up on one day, it tends to be speeding up the next day, too,' said Judah Levine, a physicist and a fellow of the National Institute of Standards and Technology in the time and frequency division.
While one short day doesn't make any difference, Levine said, the recent trend of shorter days is increasing the possibility of a negative leap second.
The prospect of a negative leap second raises concerns because there are still ongoing problems with positive leap seconds after 50 years, he explained.
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