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This summer, the Earth is spinning faster, making the days slightly shorter, attracting the attention of scientists and timekeepers.
July 10 was the shortest day ever, under 24 hours, under 1.36 milliseconds, according to data from the International Earth Rotation and Reference Systems Service and the US Navy Observatory compiled by Timeanddate.com. Furthermore, very short days are coming on July 22nd and August 5th. It is currently forecast to be 1.34 and 1.25 msec shorter than the 24 hours, respectively.
The length of the day is the time it takes for a planet to complete one full rotation on the axis – 24 hours or an average of 86,400 seconds. However, in reality, each rotation is slightly irregular due to a variety of factors, including the gravitational pull of the moon, seasonal changes in the atmosphere, and the effects of the Earth’s liquid core. As a result, a full spin usually takes just a little or just a little 86,400 seconds. This is a millisecond inconsistency that does not have a clear impact on everyday life.
However, these inconsistencies can affect computers, satellites and communications in the long run. Therefore, even the smallest deviations are tracked using an atomic clock introduced in 1955.
Atomic clocks count the vibrations of atoms held in the vacuum chamber within the clock itself, and calculate 24 hours with maximum accuracy. Calls the result time UTC or adjusted universal time. This is based on about 450 atomic clocks, and is the global standard for timekeeping, the time when all mobile phones and computers are set.
Astronomers can also use satellites that check the location of planets compared to fixed stars, for example, to track the rotation of the Earth and detect the small difference between the time of the atomic clock and the time it actually takes for the Earth to complete its full rotation. Last year, on July 5, 2024, Earth experienced the shortest day recorded in less than 24 hours in 1.66 msec since the atomic clocks appeared 65 years ago.
“We’ve been heading for a slightly faster day since 1972,” said Duncan Agnew, professor emeritus of geophysics at the Oceanographic Institute and research geophysicist at the University of California, San Diego. “But there’s fluctuations. It’s like looking at the stock market. There’s a long-term trend, then there’s a peak and a fall.”
In 1972, after decades of rotation rotated relatively slowly, Earth’s spin accumulated such delays compared to atomic time, requiring international Earth’s rotation and reference system services to add a “second” to UTC. This adds an extra day to February every four years to explain the contradictions of the Gregorian calendar and the time it takes to complete one orbit around the sun.
Since 1972, UTC has added a total of 27 jump seconds, but the additional speed has been slower and slower due to the Earth’s speedup. Nine leap seconds were added throughout the 1970s, but no new leap seconds have been added since 2016.
In 2022, the General Assembly on Weight and Major (CGPM) voted to retire from the second jump by 2035. This means that nothing else will be added to the watch. However, according to Agnew, if the Earth continues to rotate faster for several more years, it may eventually need to remove a second from UTC. “There were no negative leaps,” he said.
Agnew said the shortest change in Earth’s rotation comes from the moon and tide. This will allow the satellite to rotate faster when it is above the equator and faster when it is at altitude or at a lower altitude. This effect is exacerbated with the fact that it naturally rotates faster during the summer Earth. This is the result of the atmosphere itself slowing down due to seasonal changes, such as jetstreams moving north or south. The laws of physics indicate that the rotational speed lost by the atmosphere is picked up by the planet itself, as the Earth’s overall angular momentum and its atmosphere must remain constant. Similarly, for the past 50 years, the Earth’s liquid core has also slowed down, with the solid Earth around it getting faster.
By looking at the combination of these effects, scientists can predict whether the next day will be particularly short. “These fluctuations have a short correlation: if the Earth is speeding up on one day, it tends to speed up the next day,” said Judas Levine, a fellow at the National Institute of Standards and Technology in the division of time and frequency. “But that correlation disappears when spaced longer and longer. And once you reach a year, forecasts become very uncertain. In fact, international Earth rotation and reference system services are less predicted in advance than in a year.”
One short day makes no difference, but the recent trends on short days have increased the second most negative leap. “When the Leap second system was defined in 1972, no one really thought that a negative second would happen,” he pointed out. “It was just a standard because you had to do it for integrity. Everyone thought that only positive jump seconds were needed, but now they’re at risk of a shortening of sunrise (negative jump seconds).”
The outlook for a negative jump raises concerns as there are still issues with positive jump issues in 50 years, Levine explained. “There are places where you do the wrong thing, do it at the wrong time, make the wrong number, etc. And it repeats two seconds ago, this has been done over and over again.
So many basic technology systems are perfect for Y2K problems as they rely on clock and time, including the emergence of negative leap similar to Y2K problems, such as telecommunications, financial transactions, electrical grids, GPS satellites, and more, to name a few. From ’99’ to ’00.
Climate change is also a contributing factor to the jumping issue, but it is an incredible way. Global warming has had a major negative impact on the planet, but when it comes to our timekeeping, it helped us counter the forces that are accelerating the Earth’s spin. Agnew, published last year by Agnew, detailed in Nature Nature that ice melting in Antarctica and Greenland spreads across the ocean, slowing the Earth’s rotation.
“If that ice wasn’t melting, if there wasn’t global warming, it would be very close to having already jumping and leaping,” Agnew said. According to NASA, Meltwater from the Greenland and Antarctic ice sheets is responsible for a third of global sea level rise since 1993.
This mass shift in melted ice causes changes not only to the rotational speed of the Earth, but also to its axis of rotation, according to a study led by Benedict Soja, an assistant professor at the Federal Institute of Technology in Switzerland. If global warming continues, its effects can dominate. “By the end of this century, in a pessimistic scenario (humans continue to release more greenhouse gases) The effects of climate change could outweigh the effects of the moon that have actually driven the Earth’s rotation over the last hundreds of millions of years,” Soja said.
At this point, given the uncertainty of long-term predictions about Earth’s spinning behavior, it could lead to more time to prepare for action. “I think (faster spins) are still within reasonable boundaries, so that might be natural variation,” Soja said. “Maybe after a few years, I could see another situation again, and in the long run, I could see the planet slowing down again. That’s my intuition, but you’ll never know.”
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