The length of the day on Earth is getting longer and scientists can’t explain why

Les journées sur Terre deviennent-elles plus longues ? © Qimono, Pixnio

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[EN VIDÉO] Interview: Can we really define time? We are faced with the notion of time every day, but do we really know how to define it? This abstract concept remains a real tour de force to grasp. Futura-Sciences interviewed physicist Etienne Klein to give us an answer. Atomic clocks combined with precise astronomical measurements have recently revealed that the length of a day on Earth is suddenly lengthening. This phenomenon has critical implications not only for our measurement of time, but also for things like GPS and other technologies that govern our modern life, which determines the length of a day, has accelerated. This trend has shortened our days; in fact, in June 2022 we hit the record for the shortest day in about half a century, but despite this record, since 2020 this steady acceleration has curiously turned into a deceleration: the days are getting longer again, and the default reason for the unknown timing. If the clocks in our phones indicate that a day has exactly 24 hours, the actual time it takes for the Earth to make just one rotation varies very slightly. These changes occur over periods ranging from millions of years to almost instantaneously, even earthquakes and storms can play a role. So it turns out that a day very rarely corresponds to the magic number of 86,400 seconds. the moon. This process adds about 2.3 milliseconds to the length of each day every century. A few billion years ago, a day on Earth lasted only 19 hours. Over the past 20,000 years, another process has worked in reverse, speeding up the Earth’s rotation. At the end of the last ice age, the melting of the polar ice caps reduced the pressure on the surface, and the Earth’s mantle began to move steadily toward the poles, just as a ballet dancer spins faster when approaching arms in his. body – the axis around which it rotates – the rotation speed of our planet increases when this mantle mass approaches the Earth’s axis. And this process shortens every day by about 0.6 milliseconds per century. With decades and more, the connection between the Earth’s interior and surface also comes into play. Large earthquakes can change the length of the day, although usually by small amounts. For example, the great 2011 Tōhoku earthquake in Japan, with a magnitude of 8.9, would have accelerated the Earth’s rotation by a relatively small 1.8 microseconds. Outside of these large-scale changes, over shorter periods of time, weather and climate also have large impacts. in the rotation of the Earth, causing variations in both directions. Bimonthly and monthly tidal cycles move mass around the planet, causing changes in day length of up to a millisecond in either direction. We can observe tidal variations in day length records for periods of up to 18.6 years. The movement of our atmosphere has a particularly strong effect, and ocean currents also play a role. Snow cover and seasonal precipitation, or groundwater extraction, change things even more. Using radio telescopes to measure Earth’s rotation involves observing radio sources such as quasars. Enable French subtitles by clicking the cogwheel, then Auto-Translate, then Choose Language. © Nasa, Goddard Why is the Earth suddenly slowing down? Since the 1960s, when radio telescope operators around the planet began devising techniques to simultaneously observe cosmic objects such as quasars, we have had very precise estimates of the speed of rotation of the Earth. A comparison between these estimates and an atomic clock revealed an apparently increasingly shorter day length in recent years, a rotation that we know occurs due to tides and seasonal effects. Although Earth reached its shortest day on June 29, 2022, the long-term trajectory appears to have changed from shortening to lengthening since 2020. This change is unprecedented in the last 50 years. The deadline appears to have changed from shortening to lengthening since 2020. This change is unprecedented in the last 50 years. The reason for this change is not clear. It may be due to changes in weather systems, such as back-to-back La Niña weather events, although they have happened before. It could be an increase in the melting of the ice caps, although these have not deviated much from their usual rate of melting in recent years. Could it be related to the great explosion of the Tonga volcano injecting large amounts of water into the atmosphere? Probably not, since it happened in January 2022. Scientists have speculated that this recent and mysterious change in the planet’s rotation rate is related to a phenomenon called the “Chandler wobble,” a small deviation of the rotation axis of the Earth with a period of about 430 days. Radio telescope observations also show that the oscillation has decreased in recent years; the two phenomena could be related. A final possibility, which seems plausible to us, is that nothing specific has changed on Earth or around it. They could simply be long-term tidal effects working in parallel with other periodic processes to produce a temporary change in the Earth’s rotation rate. Do we need a “second negative interleaver”? Accurate knowledge of the Earth’s rotation rate is crucial for many applications: navigation systems such as GPS would not work without it. Also, every few years, timekeepers insert leap seconds into our official timescales to ensure they are out of sync with our planet. If the Earth moves to even longer days, we may need to incorporate a “second negative interleaver”. – which would be unprecedented and could break the Internet. The need for negative leap seconds is considered unlikely at this time. For now, we can rejoice in the news that, at least for a while, we all have a few extra milliseconds each day. Interested in what you just read?
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