Atomic clocks, combined with precise astronomical measurements, revealed that the length of a day is suddenly getting longer, and scientists don’t know why.
This has critical effects not only on our timekeeping, but also on things like GPS and other technologies that govern our modern lives.
Over the past few decades, the Earth’s rotation around its axis has accelerated, which determines how long a day is. This trend shortens our days; actually, in June 2022 we broke the record for the shortest day in the last half century.
But despite this record, that steady acceleration since 2020 has curiously turned into a slowdown – the days are getting longer again, and the reason remains a mystery until now.
While the clocks on our phones show that there are exactly 24 hours in a day, the actual time it takes for Earth to complete a single rotation changes very little. These changes occur almost instantly over millions of years – even earthquakes and storm events can play a role.
It turns out that very rarely a day is exactly the magic number of 86,400 seconds.
ever-changing planet
Over millions of years, the Earth’s rotation has been slowing due to the frictional effects associated with the tides caused by the waters. moon. This process adds about 2.3 milliseconds to the length of each day per century. A few billion years ago, only one Earth day 19 hours.
For the past 20,000 years, another process has been working in the opposite direction that has accelerated the Earth’s rotation. As the last ice age ended, melting polar ice sheets lowered surface pressure, and Earth’s mantle began to continually move toward the poles.
Just as a ballerina spins faster as she brings her arms around her body—the axis on which they spin—our planet spins faster as this mantle mass approaches Earth’s axis. And this process shortens each day by about 0.6 milliseconds per century.
For decades and more, the connection between the Earth’s interior and its surface also comes into play. Large earthquakes, although normally in small amounts, can change the length of the day.
For example, the 8.9 magnitude Great Tōhoku Earthquake that occurred in Japan in 2011 is believed to have accelerated the Earth’s rotation at a relatively small rate. 1.8 microseconds.
Alongside these large-scale changes, weather and climate over shorter periods of time also have significant effects on Earth’s rotation, causing changes in both directions.
Biweekly and monthly tidal cycles move mass around the planet, causing changes in the length of the day by up to one millisecond in either direction. We can see the tide variations In day length records over long periods such as 18.6 years.
The movement of our atmosphere has a particularly strong influence, and ocean currents also play a role. Seasonal snow cover and precipitation or groundwater removal change things even more.
Why is the world suddenly slowing down?
Since the 1960s, operators of radio telescopes around the planet have been observe cosmic objects like quasars at the same timeWe have very precise estimates of the Earth’s rotational speed.
A comparison between these predictions and an atomic clock has revealed a seemingly shorter day length over the past few years.
But when we remove the spin velocity fluctuations that we know are caused by tides and seasonal effects, there’s a surprising explanation. Despite reaching Earth’s shortest day on June 29, 2022, the long-term trajectory appears to have shifted from shortening to elongation since 2020. This change is unprecedented in the last 50 years.
The reason for this change is not clear. This may be due to changes in weather systems with back-to-back La Niña events, although this has happened before. The melting of ice sheets may be increased, but they have not deviated greatly from the steady melting rate of recent years.
Could it be related to the big volcanic eruption in Tonga? injecting large amounts of water into the atmosphere? Probably not, given that it occurred in January 2022.
Scientists have speculated This last, mysterious change in the planet’s rotation rate is related to a phenomenon called the “Chandler wobble” – a small deviation of about 430 days in Earth’s rotational axis.
Observations from radio telescopes also show that wobble has decreased in recent years; the two may be linked.
One final possibility that we think is plausible is that nothing specific has changed in or around the Earth. There can be long-term tidal effects that work in tandem with other periodic processes to produce a temporary change in the rate of Earth’s rotation.
Do we need a ‘negative leap second’?
A thorough understanding of the Earth’s rotation rate is essential for a number of applications – navigation systems like GPS simply won’t work without it. Also, every few years timekeepers add leap seconds to our official timelines to make sure they don’t get out of tune with our planet.
If the Earth were to shift to even longer days, we might need to add a “negative leap second” – that would be unprecedented and can break the internet.
The need for negative jump seconds is currently considered unlikely. For now, we can welcome the news that we all have a few extra milliseconds each day, at least for a while.
matte kingDirector of the ARC Australian Center of Excellence in Antarctic Science, University of Tasmania and Christopher WatsonSenior Lecturer, School of Geography, Planning and Spatial Sciences, University of Tasmania.
This article has been republished from: Speech Under Creative Commons license. To read original article.
