Earth's Rotation Is Speeding up this Summer. Here's Why
A millisecond, or one thousandth of a second, is admittedly not much—an eyeblink takes about 100 milliseconds. But with atomic clocks tracking the Earth's rotational speed so closely that once every year and a half or so, the International Earth Rotation and Reference Systems Service (yes, there is such a thing) has to add a leap second to the year to account for any increase in the planet's speed, every millisecond counts. So what's behind the sudden speed-up and what effect could it have?
The shortest day in history
Around the world, there are 450 atomic clocks in operation, tracking the time with an accuracy that sees them gaining or losing only about 1 second every 100 million years. The clocks exist for more than just tidy temporal bookkeeping. Everything from weather satellites to GPS satellites to telecommunications to nuclear missiles and other weapons of war rely on precise timing to operate properly. So when both astronomers and the operators of the clocks notice that the atomic ticks are falling out of step with the rotation of the Earth, people take notice.
The shortest day ever recorded since atomic clocks went into operation in the 1950s occurred last year, on July 5, according to Date and Time, when the Earth shaved off 1.66 milliseconds. Three years earlier, on June 30, 2022, things moved similarly quickly, when the day came in 1.59 milliseconds under the 24-hour wire. But with three short days predicted over the next few weeks by astronomers and clock watchers, this summer is something even more rare.
What makes Earth spin faster?
There are a number of reasons the Earth may be changing its speed this way. But it's not clear yet just which explanation is responsible this time.
The likeliest cause is the position of the moon. Lunar distance is an always-changing thing, with the moon tracing an elliptical orbit around the Earth. At its closest approach—or perigee—the moon is only 224,000 miles distant. At its furthest—or apogee—that gap widens to 251,655 miles. On the three speedy days this summer, the moon will be at or near apogee—which is a puzzle, since lunar gravity is such that the Earth tends to slow down, not speed up, when the moon is farther away.
The moon's orbit is not only elliptical, however, but cockeyed too, angled anywhere from 18° to 28° relative to the Earth's equator. The sharper that angle is the faster the Earth orbits, with lunar gravity in this case speeding things up, countering the braking effect that lunar apogee usually applies. On the three days in question this summer, the moon will be close to its 28° peak.
The moon is not the only thing that can shorten earthly days. Earthquakes can too, redistributing subterranean mass and causing the planet to accelerate or slow down in the same way a figure skater can change the speed of her spin when she tucks in or extends her arms. In 2005, an earthquake in Indonesia shifted the Earth's polar mass about one inch toward the east, decreasing the length of a day by 2.68 microseconds—or millionths of a second. No significant earthquake has occurred recently, however, ruling temblors out as the cause of the current speed up.
Does climate change impact Earth's rotation?
Climate change—again and seemingly always—may play a role too. Last year, two NASA-funded studies found that since 2000, melting glaciers have caused the axis of the planet—or the centerpoint of its spin—to shift by about 30 ft., changing the speed of rotation. The catch is, in this case the change causes the planet to decelerate, not speed up—by about 1.33 milliseconds per century. If warming continues at its present pace, it is projected to increase the length of our days by 2.62 milliseconds by the end of the century.
Other factors, including rising ocean levels and the warming—and thus swelling—of the atmosphere can make a difference too, slightly increasing planetary circumference. Even the springtime blossoming of trees can play a role. 'In northern summer, the trees get leaves,' geophysicist Richard Holme of the University of Liverpool told Live Science. 'This means that mass is moved from the ground to above the ground—further away from the Earth's spin axis.' In all of these cases too, however, the effect is to slow the Earth, not speed it up.
So that brings scientists back to lunar gravity as the cause of the current acceleration—and that's a reason not to fret the slightly shorter days. The Earth and the moon have been doing their dance for the better part of 4.5 billion years, and it's always been a stable one. Here's betting they've got a few billion more years yet in their run.
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Yahoo
31-07-2025
- Yahoo
Why Earth Is Rotating Extra Fast This Summer, Shortening Days by Milliseconds
As Earth spins through space, its rate of rotation changes. Here's why If you haven't accomplished as much this summer as you had hoped to, you can blame forces far beyond your control: a few of these dog days, by one measure, are among the shortest you've ever lived through. For most of humanity's history, we have measured time by the sun as it rises and sets—essentially, through Earth's orientation to the cosmos surrounding us. But compare that technique with modern, superprecise timekeeping, and soon you'll find that each day varies a bit in length at the scale of thousandths of a second. This summer a few factors are adding up to make a handful of Earth's spins—those occurring on July 10, July 22 and August 5—more than a millisecond faster than the average of the past several decades. Yes, there are scientists whose job is to track these things; no, they are not particularly concerned by these developments. 'It's a very small phenomenon,' says Christian Bizouard, an astronomer at the Paris Observatory and primary scientist at the International Earth Rotation and Reference Systems Service's Earth Orientation Center. 'There is nothing extraordinary [happening].' [Sign up for Today in Science, a free daily newsletter] Bizouard has a point, of course—no one is going to notice the sun rising a millisecond earlier or later than we might otherwise expect. But tracking Earth's rotation to this level of precision is vital because countless aspects of modern life rely on our ability to pinpoint locations to within a meter, and high-precision GPS navigation requires that satellites know exactly where they are compared with features on Earth's surface. So Bizouard and his colleagues track Earth's orientation in space. To do so, they have enlisted astronomers all over the planet to monitor a collection of about 300 objects, he says, primarily the bright, very distant, supermassive-black-hole-powered objects known as quasars. All day, every day, pairs of distant observatories tuned to radio wavelengths of light check in on their specific object. By measuring the timing mismatch between light received at each station, scientists can calculate the precise location of the observatories and, in turn, the planet. That's how scientists know that the amount of time it takes Earth to complete one rotation varies slightly. But why does the planet's speed vary? Even if you may never notice their loss, the missing milliseconds offer us a glimpse into the intricate oddities of the planet we live on—so let's track them down. Officially, time is defined by nine-billion-some vibrations of a cesium atom per second, 86,400 seconds per day. Inconveniently, Earth's behavior isn't governed by cesium atoms. Physics holds that, as a solid object moving in a vacuum, Earth ought to keep spinning at the same rate unless some outside force intervenes, says Duncan Agnew, a geophysicist at the Scripps Institution of Oceanography. But Earth isn't quite a simple solid object, and it has a rather large moon that can provide outside force. That means several different factors can affect Earth's rotation speed. Two of these factors—the core and the atmosphere—each affects Earth's spin under a similar principle. The overall rotational speed of the Earth system must stay steady, so if a component's movement changes, then the overall planet has to compensate. 'The sum of all the rotations has to add up to the same thing,' Agnew says. 'If part of the Earth is going slower, another part has to go faster.' Take Earth's core, for example, hiding below what we think of as the solid ground we walk on. Only the inner portion of the core is actually solid; the rest is fluid. 'There's this giant ball of molten iron about the size of the moon inside the Earth,' Agnew says. All that liquid metal (there's a little nickel mixed in with the iron) is moving, creating the magnetic field that shields us from some of the many hazards of space. The core's activity is quite a mystery. The region isn't actually all that far away—less than 2,000 miles from the surface, closer than New York City is from Los Angeles—but it cannot be directly accessed and is therefore very difficult to understand. In recent decades, for whatever reason, the core's spin has been slowing, forcing the rest of Earth to speed up to compensate. 'The core is what changes how fast the Earth rotates on periods of 10 years to hundreds of years,' Agnew says. 'The core has been slowing down for the last 50 years, and as a result, the Earth has been speeding up.' (This speed-up is part of why timekeepers have not implemented an artificial leap second—a tactic used annually during small stretches of the late 20th century—since 2016 and don't expect to anytime soon.) A similar phenomenon plays out in Earth's atmosphere. Like the core, the atmosphere is a fluid mass—and although it's a very complex one, scientists have much better insight into it than into the elusive core. The atmosphere changes with the seasons as the sun's radiation falls disproportionately on different parts of the planet. The Northern and Southern Hemispheres each have a primary polar jet stream, a river of strong wind flowing from west to east that wanders north and south as it carries weather around the planet. Because of Earth's topography and the influence of ocean currents, the Southern Hemisphere's jet stream is stronger overall than the Northern Hemisphere's. And each jet stream is fastest during its hemisphere's winter, slowing somewhat in local summer. Combine those factors and the Northern Hemisphere summer sees a small decrease in total speeds of westerly wind (those flowing west to east), Agnew says—forcing the solid Earth to spin a smidge more rapidly to compensate. This atmospheric effect is why the rotation rate changes in an annual cycle, with the days when Earth rotates fastest tending to cluster in the Northern Hemisphere's summer, particularly July and August. To the extent that the core explains decadal changes and the atmosphere explains annual ones, the moon explains millennial and daily differences in Earth's rotation rate. At geologic timescales, Earth's rotation is slowing down because of the moon's tidal influences on the water that fills our planet's oceans. The moon's gravity sloshes water around, causing an infinitesimal friction between ocean and seafloor. 'That's been slowing the Earth down since the Earth had oceans,' Agnew says. This trend doesn't register to humans, but over time, the effect is quite noticeable. About 70 million years ago, shortly before the extinction of nonavian dinosaurs, a day was about half an hour shorter than it is today, for example. Wind the clock even further back, to 245 million years ago, when dinosaurs first came on the scene, and a day lasted a bit more than 22 and a half hours, scientists have calculated. The moon causes a second phenomenon that affects Earth's rotation on a human timescale. Beachgoers know full well that the moon's gravity causes the seas' daily high and low tides, and the solid Earth rises and falls a little bit in response to the moon as well, albeit not nearly as noticeably. But the moon's orbit doesn't line up with Earth's equator: our constant companion's path is a bit tilted compared with Earth. Because of this, the tidal bulges wander north and south over the course of the moon's loops around Earth. When the moon is right over the equator, the tidal bulges are, too, and therefore their mass is farther away from the planet's spin axis; when the moon is the farthest north or south, the bulges move away from the equator, slightly closer to the planet's spin axis. This taps into the same physics as a spinning ice skater with outstretched arms does when they hug their chest to speed up—Earth's rotation rate speeds up just a hair when the moon is at the northernmost or southernmost point in its orbit, about every two weeks. All these factors combine for the remarkably complicated state of Earth's rotation rate: it is slowing over geologic time because of ocean friction but has been speeding up over recent decades because of the core, and its spin speed slightly increases every summer from the atmosphere and every two weeks from the moon's north-south wandering. The changes make such good sense in terms of physics that scientists like Bizouard are able to take variations in Earth's rotation rate for granted. And scientists have some grasp of the annual and weekly changes in Earth's spin rate, allowing them to expect the speedy summer days. But the mysteries of Earth's core prevent these experts from confidently charting how Earth's rotation will change into the future. 'We are not able to predict anything,' Bizouard says. Scientists put out predictions anyway, of course. As summer approached, they thought August 5 might be the shortest day of the year, a full 1.5 milliseconds shorter than usual. Current estimates still indicate that this day will be about that much shorter, and that August 18 may be another contender for the year's fastest rotation. For comparison, the shortest rotation day in recent years was on July 5, 2024, when we lost 1.66 milliseconds. Yes, you've probably now spent more time wrapping your mind around Earth's quickest days than you've ever lost to the vagaries of our planet's spin; I know I have. Let's just call it another reason why we live on the most remarkable planet out there. Solve the daily Crossword
Scientific American
28-07-2025
- Scientific American
Summer Meteor Showers, Short Summer Days and Ancient Arthropods
Rachel Feltman: Happy Monday, listeners! For Scientific American 's Science Quickly, I'm Rachel Feltman. It's been a while, but we're finally back with our usual science news roundup. Let's catch up on some of the science news you might have missed in the last week or so. If last Tuesday seemed to fly right by, that's probably because it was a little shorter than usual. The International Earth Rotation and Reference Systems Service says that July 22 was around .8 milliseconds short of the standard 24 hours. That's slightly less dramatic than the almost 1.4 milliseconds that were missing from July 10, and scientists anticipate another ever-so-slightly truncated day on August 5. Now, while there were plenty of headlines about these missing fractions of a milliseconds, it's not actually news that the Earth's rotation varies in speed. The length of a single rotation—also known as a day—is impacted by factors such as the movements of our planet's liquid core, variations in the jet stream and the gravitational pull of the moon. One 2024 study even suggested that melting polar ice has decreased Earth's angular velocity enough to slow rotations down. On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. In fact, earth's days have generally been trending longer if you look back at the last few billion years. Research suggests that at various points in the time before our species evolved, days were minutes and even hours shorter. But we always get our shortest days in the summer, and there have been some especially short ones over the last few years. Scientists aren't totally sure why that's been happening, but they expect the spike to flatten back down soon, according to reporting by The Guardian. Speaking of the movement of celestial heavenly bodies: two meteor showers are set to peak on the same evening this week. In the overnight from July 29 to 30 both the Southern delta Aquariids and the alpha Capricornids will be reaching the height of their activity. While the alpha Caricornids aren't known for dropping loads of visible objects, they do sometimes produce bright fireballs—plus they can be seen from anywhere on the planet. Meanwhile, folks in the Southern Hemisphere will also get a great view of the Southern delta Aquariids, and people farther north could catch some activity if they look southward. There will also be some scattered meteors from the Perseids, which will ramp up in activity next month. With the moon in a waxing crescent phase, conditions should be good for spotting meteors—as long as it's not too cloudy. So set an alarm for the predawn hours on Wednesday and go outside to take a peek. Now let's head back down to Earth. Last Monday the Federal Emergency Management Agency's Urban Search and Rescue chief resigned. Ken Pagurek, who spent more than a decade with the FEMA branch and served as its chief for about a year, reportedly told colleagues that his decision was motivated in part by the delayed response to Texas's recent catastrophic flooding. The Department of Homeland Security recently implemented a policy that requires Secretary Kristi Noem to personally approve any spending over $100,000. CNN reports that Noem took more than 72 hours to provide authorization for Urban Search and Rescue teams to deploy in Texas. According to the New York Times, Noem also failed to renew agreements with call center companies whose contractors would have answered calls from disaster survivors. The contracts lapsed in the aftermath of the flood, when many people were still in need of help. The Times reported on July 5, FEMA received a bit more than 3,000 calls and answered about 99.7 percent of them. On July 6, with hundreds of the contractors responsible for answering phones suddenly fired, FEMA reportedly received 2,363 calls and answered about 35.8 percent of them. And according to the Times, those contracts weren't renewed until July 10. When asked for comment on Pagurek's resignation by ABC News, a DHS spokesperson doubled down on the new spending policy, defending the agency's decision not to 'hastily approve a six-figure deployment contract without basic financial oversight.' Let's pivot to some health news. According to a study of nearly 1,000 people published last Tuesday in the journal Nature Communications, the COVID pandemic may have made our brains age more quickly—regardless of whether we got sick. First, the researchers analyzed imaging from more than 15,000 healthy individuals collected pre-pandemic to establish a baseline for normal brain aging. The team used this data to train machine-learning models to predict a person's brain age based on certain structural changes. The researchers then applied those models to brain scans from 996 other subjects, all of whom had received two brain scans at least a couple of years apart. About half of the participants had received both scans prior to the start of the pandemic, so they served as the control group. The scientists were then able to look at scans taken before and after the pandemic to assess the rate of brain aging. While only folks who got infected with COVID between their two scans showed a dip in some cognitive abilities, signs of brain aging, such as the shrinkage of gray matter, were accelerated across the board. The effects were most pronounced among men, older individuals and people from more socioeconomically deprived backgrounds. The study authors pointed to a number of aspects of the pandemic—including increases in stress, alcohol consumption and economic insecurity, along with decreases in physical activity and socialization—that they believe may have made our brains age more quickly. We don't yet know what the implications of these changes might be or whether they're reversible. Speaking of brains—and to end our show on a fun story because you know I love to do that—let's talk about ancient sea critters. A recent study focused on the extinct species Mollisonia symmetrica, which lived around half a billion years ago, suggests that the ancestors of spiders and other arachnids may have started out in the ocean. In studying fossilized remains of the tiny creature, scientists found that its brain was basically backwards—at least compared to other arthropods. The layout is more similar to the way modern arachnid noggins are arranged, which suggests that spider brains may have first evolved in the sea. That's all for this week's news roundup. We'll be back on Wednesday to talk about some of this summer's hottest topics in the world of weather. Science Quickly is produced by me, Rachel Feltman, along with Fonda Mwangi, Kelso Harper and Jeff DelViscio. Shayna Posses and Aaron Shattuck fact-check our show. Our theme music was composed by Dominic Smith. Subscribe to Scientific American for more up-to-date and in-depth science news.
Newsweek
10-07-2025
- Newsweek
Earth's Rotation Sped Up on July 9—and We're Not Sure Exactly Why
Based on facts, either observed and verified firsthand by the reporter, or reported and verified from knowledgeable sources. Newsweek AI is in beta. Translations may contain inaccuracies—please refer to the original content. If you've felt like summer days are flying by, you're not wrong—at least not scientifically. Experts have observed that Earth's rotation is speeding up, making some days slightly shorter than the standard 24 hours. On July 9, 2025, scientists at the International Earth Rotation and Reference Systems Service (IERS) reported that the Earth completed its rotation approximately 1.3 to 1.6 milliseconds faster than the standard 24-hour period. Moreover, this is expected to happen again on July 22 and August 5 this year. While the differences in time are imperceptible to humans, it's significant enough to raise eyebrows in the world of ultra-precise timekeeping. It takes Earth 24 hours, or 86,400 seconds, to make one full rotation around its axis, but Earth's rotation isn't perfectly constant. It speeds up and slows down due to a complex mix of factors, and scientists monitor these fluctuations using atomic clocks. These clocks are so accurate that they only lose or gain a second every 100 million years. Why is Earth spinning faster? "The causes of the recent acceleration are not fully understood," Astrophysicist Graham Jones told Newsweek. There's no single reason why Earth is spinning faster, but scientists point to several likely contributors. One major factor is the Moon. Earth's natural satellite exerts a powerful gravitational pull that generally slows our rotation over long timescales. But during certain points in the Moon's elliptical and tilted orbit, especially when it's farthest from Earth and at its steepest angle relative to the equator, lunar gravity can have a speeding effect. On the key dates this summer, the Moon will be near its farthest point and at a sharp orbital tilt—conditions that appear to align with these shorter days. Another key factor is the constant exchange of angular momentum between different parts of the Earth system. "If the atmosphere speeds up, the solid Earth slows down—and vice versa," geophysicist professor Richard Holme of the University of Liverpool told Newsweek. Over longer periods, similar exchanges occur between Earth's mantle and its fluid core. A file photo of a globe spinning. A file photo of a globe spinning. Stockbyte/Getty Images Other factors thought to impact the speed of the Earth's spin include geological activity, like earthquakes, which can redistribute the planet's mass and affect its spin, though there are no recent large quakes to link to this year's speed increase. Glaciers melting as a result of climate change can also shift water masses around the planet, altering Earth's axis, though this is usually expected to slow the planet's rotation rather than speed it up. "Studies support the idea that the redistribution of ice and water affects Earth's rotation, although this likely doesn't explain the recent acceleration," Jones said. What are the implications? It may sound like cosmic trivia, but the consequences of Earth's rotational changes are real. "If this faster rotation continues, a negative leap second may be required to keep our clocks in sync with the Sun. This would mean a second is skipped—there would be a minute with only 59 seconds," Jones explained. This would cause problems for global infrastructure like satellite navigation, military systems and global financial markets that rely on split-second precision. A mismatch between the planet's rotation and atomic time could wreak havoc on these networks. "For navigation, GPS is corrected for position for an offset caused by a cumulative effect of change in rotation rate. For timekeeping systems, there is mention of possibly adopting a negative leap second—an extra (or in this case, one fewer) second in the day to make sure we line up again," Holme said. To date, all adjustments to time have involved adding a leap second. But if Earth's current acceleration continues, scientists may soon need to subtract one instead, a move that could pose new challenges for timekeeping systems and software. Is Earth speeding up? The shorter days noticed by scientists have sparked interest, but in general, the Earth is slowing in rotation. "There were 400 days in a year 300 million years ago, for about the same length of year," Holme explained. "Overall, the Earth's rotation is slowing," Jones agreed. "But within this overall pattern, there are ups and downs in Earth's rotational speed." Do you have a tip on a science story that Newsweek should be covering? Do you have a question about Earth's rotation? Let us know via science@
