Earth took 1.59 milliseconds faster to make a full rotation on June 29 than the usual 24 hours. This is a record time since measurements began in the 1960s. In other words, June 29 was the shortest day ever recorded. The previous record was on July 19, 2020 only.
So it turns out that it is not a one-time fact, that the speed of the Earth’s rotation around its axis. In 2020, the shortest 28 days were recorded since the measurements were kept. Also in 2021 and 2022 it was sometimes faster than usual. Recently, on July 26, 2022, the Earth was 1.5 milliseconds ahead of the daily schedule.
According to Judah Levine, a professor at the University of Colorado Boulder and a physicist at the National Institute of Standards and Technology, we’re likely to get more of those short days because the Earth apparently keeps spinning faster. The expert says panic is definitely not necessary, as it only concerns a fraction of a second on a yearly basis. What is remarkable is that scientists have no real explanation for the current slight acceleration of the Earth’s rotation.
In principle, the speed of the Earth’s rotation decreases in the long run. This is because of the Moon, which is responsible for the tides on our planet and thus creates friction as well as delays. A few hundred million years ago, for example, a day lasted only 22 hours and a day is expected to last for thousands of years longer than — roughly — 24 hours today. So the acceleration in recent years goes against this trend.
It is the International Earth Rotation and Reference Systems Service that measures the speed of Earth’s rotation. The speed does not quite correspond to the exact 24 hour period, which we assign to a solar day. This led to the introduction of the leap second in 1972. Essentially, when the Earth’s rotation is out of sync with atomic clocks and the deviation threatens to exceed one second, scientists turn off the clocks for a second on June 30 or December 31 at 11:59 PM to adjust. The last time this happened was on December 31, 2016.
negative jump again
Since then it is no longer necessary because an acceleration of the Earth’s rotation has been recorded in the past two years rather than a slowdown. There is now talk of a possible negative jump second to set the atomic clock. “If this acceleration continues — and this is a significant ‘if’ sign — we may need a second negative jump in about seven to eight years,” Levine says.
This may have something to do with the so-called “Chandler’s wobble,” which was discovered in the 19th century. This phenomenon explains why a not perfectly round Earth oscillates slightly and thus slowly rotates on its axis. According to Leonid Zotov, this wobble mysteriously disappeared between 2017 and 2020, causing the Earth to spin a little faster again.
Another possible explanation is that climate change will affect the speed of Earth’s rotation. The melting of glaciers slightly changes the shape of the Earth: it is flat at the poles and convex at the equator. But according to Professor Levine, melting glaciers should have the opposite effect. So the speed of the Earth’s rotation should decrease, not increase.
Levine believes that the high speed at which the Earth rotates on its axis is partly caused by the interaction between the Earth and the atmosphere. “When the atmosphere accelerates, the Earth slows down, and vice versa,” it seems. “Because the sum of the two is constant.” Levine concludes that “the speed of the Earth’s rotation is a complex issue” and that it is subject to a combination of these factors. “You cannot predict what will happen in the distant future.”
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