【By Observer Net, Chen Sijia】According to a report by the British Broadcasting Corporation (BBC) on July 22, scientists estimate that the Earth will complete one rotation slightly faster than usual today, making the length of this day shorter by about 1.34 milliseconds compared to the standard 24 hours. Prior to this, the length of the day on July 9 was shortened by 1.36 milliseconds, so July 22 will become the "second shortest day" of this year.

Scientists from the International Earth Rotation and Reference Systems Service (IERS) reported that on July 9, July 22, and August 5 in 2025, the time it takes for the Earth to complete one rotation will be approximately 1.3 to 1.6 milliseconds shorter than the standard 24-hour cycle.

Data from IERS shows that on July 9, the Earth completed its rotation 1.36 milliseconds shorter than the standard 24 hours, making it the "shortest day" of 2025. The agency predicts that on July 22, the Earth may complete its rotation 1.34 milliseconds earlier, becoming the "second shortest day" of this year; the duration on August 5 will also be shortened by about 1.25 milliseconds compared to the normal cycle.

The U.S. "Science News" website pointed out that astronomers generally believe the position of the moon is a major factor contributing to this phenomenon. During these days, the moon's position on its orbit will be farthest from the Earth's equator, reducing the effect of the moon's gravity and causing the Earth's rotation speed to increase.

Photo of the Earth NASA

The U.S. "Newsweek" stated that scientists use precise atomic clocks to monitor the time each day. Although changes of less than 1.5 milliseconds will not affect people's daily lives, these variations are enough to draw attention in fields requiring precise timing.

Currently, July 5, 2024, is the shortest day ever recorded by scientists, when the Earth completed one rotation 1.66 milliseconds faster than usual.

Duncan Agnew, a geophysicist at the University of California, San Diego, said that although this phenomenon will not cause catastrophic consequences, it is worth noting. He pointed out that if the Earth continues to rotate faster in the coming years, the global timing systems may face historic adjustments: the introduction of a "negative leap second" for the first time.

There are two commonly used time measurement systems in the world: Universal Time (UT), based on the Earth's rotation, and International Atomic Time (TAI), based on the oscillation cycle of atoms. Due to the difference in the two measurement methods, over time, the results of the two timing systems will diverge, so scientists proposed the concept of Coordinated Universal Time (UTC).

In 1972, the International Conference on Weights and Measures decided that when the difference between International Atomic Time (TAI) and Universal Time (UT) reaches 0.9 seconds, UTC would add or subtract 1 second to stay as close as possible to UT, and this correction is called a leap second. Because the Earth's rotation has been slowing down, all the leap seconds added so far have been positive leap seconds, i.e., adding 1 second.

Agnew told CNN that if the rotation continues to accelerate, it would be necessary to subtract 1 second from UTC, "there has never been a negative leap second before, but the probability of a negative leap second occurring between now and 2035 is about 40%."

However, the New York Times pointed out that due to factors such as the moon's gravity, the Earth's rotation speed has been slowing down over the past few thousand years. Therefore, scientists speculate that the phenomenon of accelerated rotation will not become a long-term trend. Professor Clark R. Wilson from the University of Texas at Austin said that the trend of the Earth's rotation slowing down is expected to continue, but this process is very slow, "so slow that it is far beyond human time scales."

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Original: https://www.toutiao.com/article/7529859149443465767/

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