Day Shortened by 1.25 to 1.36 Milliseconds
International Scientific Community Pays Attention... Possible Long-term Effects
"Cause of Acceleration Remains Unexplained"
This summer, the Earth's rotational speed increased, resulting in slightly shorter days. While this change is imperceptible in daily life, it has drawn the attention of scientists and timekeepers.
On July 21 (local time), CNN reported that, according to data collected by the International Earth Rotation and Reference Systems Service (IERRS) and the US Naval Observatory for 'Time & Date.com,' July 10 was the shortest day of the year, with the day being 1.36 milliseconds (one-thousandth of a second) shorter than the standard 24 hours. It is also predicted that August 5 will be 1.25 milliseconds shorter than 24 hours.
The length of a day is defined as the time it takes for a planet to complete one full rotation on its axis, averaging 24 hours or 86,400 seconds. However, in reality, various factors such as the Moon's gravity, seasonal changes in the atmosphere, and the liquid state of Earth's core cause slight irregularities in the duration of a day. As a result, the actual day may be slightly longer or shorter than 86,400 seconds, but discrepancies of just a few milliseconds have virtually no impact on daily life.
However, such discrepancies can have long-term effects on computers, satellites, and communications. To address this, the scientific community introduced atomic clocks in 1955 to track even the smallest deviations in time. Some experts warn that increasingly shorter days could pose serious risks. For example, they point out that a situation similar to the 'Y2K problem'?when computer systems risked misreading the year 2000 as 1900 due to date formatting errors?could occur. At that time, warnings that modern civilization could be disrupted created significant social concern.
Originally, in 1972, the IERRS decided to introduce the leap second, similar to a leap year, because the Earth's rotation was too slow compared to atomic clocks. As a result, a total of nine leap seconds were added in the 1970s. However, as the Earth's rotational speed increased, not a single leap second has been added since 2017. Ultimately, in 2022, the General Conference on Weights and Measures (CGPM) decided to abolish the leap second by 2035.
According to CNN, if the Earth's rotational speed continues to increase, there is a possibility that a 'negative leap second,' which would subtract one second from the standard 24-hour day, could be introduced. Although a negative leap second has never been implemented, it is estimated that by 2035, there is about a 40% chance this could occur.
So far, the reasons for the increase in the Earth's rotational speed have not been specifically explained. Human activities or events such as earthquakes may have affected the Earth's rotation. For example, the earthquake that struck Japan in 2011 is known to have shortened the Earth's day by 1.8 microseconds (one-millionth of a second). Conversely, some analyses suggest that the melting of glaciers due to global warming has caused the length of the day to increase by 1.3 milliseconds over the past 100 years since 2000.
Leonid Zotov, an astronomer at Moscow State University, told the science media outlet Live Science, "No one expected this to happen. The cause of this acceleration has not been explained," adding, "Most scientists believe it is something inside the Earth."
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