(ORDO NEWS) — Atomic clocks, combined with precise astronomical measurements, have shown that the length of the day is suddenly increasing, and scientists don’t know why.
This has a decisive impact 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 rotation of the Earth around its axis, which determines the length of the day, has accelerated.
This trend is making our days shorter; in fact, in June 2022 we set the record for the shortest day in the last half century or so.
But despite this record, since 2020, the steady acceleration has curiously given way to a slowdown, with the days getting shorter. again longer, and the reason is still a mystery.
Although the clocks on our phones show that there are exactly 24 hours in a day, the actual time it takes the Earth to complete one revolution varies greatly. a little.
These changes take place over millions of years or almost instantly even earthquakes and hurricanes can play a role.
It turns out that a day very rarely coincides exactly with the magic number of 86,400 seconds.
An ever-changing planet
For millions of years, the Earth’s rotation has slowed down due to frictional effects associated with tides caused by the Moon.
This process increases the length of each day by about 2.3 milliseconds every century. A few billion years ago, an Earth day lasted only about 19 hours.
For the past 20,000 years, another process has been going in the opposite direction, accelerating the Earth’s rotation.
As the last ice age ended, the melting of the polar ice sheets relieved surface pressure, and the Earth’s mantle began to steadily move toward the poles.
In the same way as a ballet dancer rotates faster, bringing his arms closer to the body – the axis. around which they revolve – so our planet’s rotational speed increases as this mantle mass approaches the Earth’s axis. And this process is reduced every day by about 0.6 milliseconds per century.
For decades and longer, the connection between the interior of the Earth and the surface also comes into play. Strong earthquakes can change the length of the day, although usually by a small amount.
For example, the 2011 Great Tohoku Earthquake in Japan, with a magnitude of 8.9, is thought to have accelerated the Earth’s rotation by a relatively tiny 1.8 microseconds.
In addition to these large-scale changes, over shorter periods, weather and climate also have an important effect on the Earth’s rotation, causing oscillations in both directions.
Biweekly and monthly tidal cycles move mass around the planet, causing changes in the length of the day down to the millisecond in either direction. We can observe variations in tides in the records of the length of the day for periods of up to 18.6 years.
The movement of our atmosphere has a particularly strong influence, and ocean currents also play a role. Seasonal snow cover and rain or groundwater extraction further change the situation.
Why is the Earth suddenly slowing down?
Since the 1960s, when operators of radio telescopes around the planet began to develop methods for simultaneously observing space objects such as quasars, we have obtained very accurate estimates of the speed of the Earth’s rotation.
Comparison of these estimates with the readings of atomic clocks showed that over the past few years, the length of the day, apparently, has been constantly decreasing. .
But there is a surprising discovery when we remove the fluctuations in rotational speed that we know are due to tides and seasonal effects.
Even though the 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 reason for this change is as follows. dont clear. This may be due to changes in weather systems, with successive La Niña events, although they have occurred before.
This may be due to increased melting of the ice sheets, although the rate of melt has not deviated much from their stable rate in recent years.
Could this be related to the huge explosion of the Tonga volcano, spewing huge amounts of water into the atmosphere? Probably not, considering it happened in January 2022.
Scientists have suggested that this recent mysterious change in the planet’s rotation rate is due to a phenomenon called the “Chandler wobble” – a slight deviation of the Earth’s axis of rotation with a period of about 430 days.
Observations from radio telescopes also show that the wobble has decreased in recent years; they may be related to each other.
The last possibility we consider plausible is that nothing much has changed in or around the Earth. These may simply be long-term tidal effects, working in parallel with other periodic processes and causing a temporary change in the speed of the Earth’s rotation.
Do we need a “negative leap second”?
An accurate understanding of the Earth’s rotational speed is critical for a variety of applications—navigation systems like GPS won’t work without it.
Also, every few years timekeepers insert leap seconds into our official timelines to make sure they don’t get out of sync with our planet.
If the Earth were to go for even longer days, we might have to turn on “negative leap second” – that would be unprecedented and could break the internet.
The need for negative leap seconds is now considered unlikely. For now, we can welcome the news that – at least for a while – we all have a few extra milliseconds every day.
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