Earth is spinning FASTER now than it was 50 years ago – and if it continues speeding up scientists may have to deduct a second from the atomic clock
- The Earth rotates on its axis more than 365 times in a single orbit of the Sun
- This is significantly less than the 420 times it rotated millions of years ago
- Even in 100 years the rotation has slowed further, with a day milliseconds shorter
- This has required leap seconds to be added to atomic clocks every few years
- No new leap seconds have been added since 2016 and there are signs the rotation of the Earth has begun to speed up again, requiring a second removed
Earth is spinning faster than it was half a century ago, and if it continues speeding up scientists say they may have to remove a second from the atomic clock.
The speed our planet rotates on its axis has varied throughout history.
In fact, Earth rotated 420 times per year millions of years ago, but now does so 365 times.
However, sometimes the speed of rotation varies slightly, affecting the global timekeeper – the atomic clock – requiring leap seconds to be added when the world runs slightly faster.
Now, UK National Physical Laboratory scientist, Peter Whibberley, has warned that if the rotation rate increases further, a negative leap second may be needed.
Earth is spinning faster than it was half a century ago, and if it continues speeding up scientists say they may have to remove a second from the atomic clock
THE EARTH ROTATES ON ITS AXIS OVER 365 TIMES EACH TIME IT ORBITS THE SUN
The rotation of the Earth, or its spin around its own axis, has varied over the 4.6 billion year history of our world.
Millions of years ago it would rotate 420 times in a single orbit of the Sun, but today that is 365.5 times.
It rotates once in about 24 hours with respect to the Sun, but once every 23 hours, 56 minutes and 4 seconds with respect to other distant stars.
It has been slowing for millions of years, although scientists have noticed a slight speeding up since 2016.
This is due to the tidal effects the Moon has on Earth’s rotation. A
tomic clocks show that a modern-day is longer by about 1.7 milliseconds than a century ago, requiring leap seconds.
Each day on Earth contains 86,400 seconds, but the rotation isn’t uniform, which means over the course of a year, each day has a fraction of a second more or less.
This is caused by the movement of the Earth’s core, its oceans and atmosphere, as well as the pull of the Moon.
The atomic clock is extremely precise, and measures time by the movement of electrons in atoms that have been cooled to absolute zero.
So, to keep the atomic clock in line with the number of seconds in the rotation of the Earth, leap seconds have been added every 18 months or so since 1972.
There has never been a negative leap second – the removal of a second from the atomic clock – and a system designed to make that work have never been tested.
The idea came up last year, when the rotation began to speed up, but this has since slowed down again, with the average day in 2021 0.39 milliseconds less than 2020.
‘As time goes on, there is a gradual divergence between the time of atomic clocks and the time measured by astronomy,’ Judah Levine from the National Institute of Standards and Technology told Discover Magazine.
‘In order to keep that divergence from getting too big, in 1972, the decision was made to periodically add leap seconds to atomic clocks.’
The International Earth Rotation and Reference Systems Service is responsible for tracking how quickly the Earth spins, and does so by sending laser beams to satellites and using that to measure their movement.
When this is out of line with atomic clocks, scientists coordinate to stop their clocks for one second to bring them back into line.
‘The rotation rate of Earth is a complicated business. It has to do with exchange of angular momentum between Earth and the atmosphere and the effects of the ocean and the effect of the moon,’ Levine explained.
‘You’re not able to predict what’s going to happen very far in the future.’
Each day on Earth contains 86,400 seconds, but the rotation isn’t uniform, which means over the course of a year, each day has a fraction of a second more or less
WHAT IS A LEAP SECOND?
A leap second is an adjustment of a single second to the Coordinated Universal Time (UTC).
This is designed to keep atomic clock time and solar time inline.
There are difference between the incredibly precise International Atomic Time (TAI) measured by atomic clocks, and the imprecise observed solar time (UT1), linked to Earth’s rotation.
UTC time standard, inline with Greenwich Mean Time (GMT) is widely used for global timekeeping, including in astronomy.
Without the leap second, added every few years, UTC would be out of line with the Earth’s rotation speed.
While this wouldn’t be noticable to most people, over hundreds of years it could shift the point of Noon, and would impact the internet.
However, it isn’t a popular practice, proving distruptive to some internet services, with Google ‘smooshing’ time over a year to add the increase in microseconds to each day.
International standards bodies responsible for time are debating whether to drop the practice, as even over 100 years it would only drift by about a minute.
There hasn’t been a leap second added to the atomic clock since 2016, and while the Earth has been speeding up again, this began to slow again in 2021.
‘This lack of the need for leap seconds was not predicted,’ Levine said.
He added that it was assumed Earth would continue to slow down, ‘so this effect,’ he said ‘is very surprising.’
How long the speed and slowing trend continues might require scientists to take further action, but it is yet unclear what that might be.
‘There is this concern at the moment that if Earth’s rotation rate increases further that we might need to have what’s called a negative leap second,’ Whibberley told Discover Magazine.
‘In other words, instead of inserting an extra second to allow Earth to catch up, we have to take out a second from the atomic timescale to bring it back into state with Earth.’
While they know how they could make it work, the scientists aren’t clear whether their systems would work in reality, or what impact they’d have.
The internet relies on the steady flow of time, measured through atomic clocks, and different web firms use different processes to whether leap seconds.
For example, Google uses a system that spreads the extra time out throughout the year, to every other second in a year.
‘The primary backbone of the internet is that time is continuous,’ Levine explained.
He added that when there is no steady time, the continuous feed of information falls apart.
Levine says leap seconds – added or removed – may not be worth the hassle, as in total they’d only add up to about a minute over 100 years.
WHAT IS THE ATOMIC CLOCK?
Atomic clocks have a timekeeping mechanism that use the interaction of electromagnetic radiation with the excited states of certain atoms.
The devices are the most accurate system we have for measuring time, with consistent standards applied.
They are the primary standards for international time distribution services, and uses to control wave frequency for TV, GPS and other services.
The principle is founded in atomic physics, measuring the electromagnetic signal that electrons ina toms emit when they change energy levels.
Modern versions cool atoms to near absolute zero by slowing the atoms down with lasers. With temperature of atoms driving their accuracy.
Every few years a ‘leap second’ is added to atomic clocks, by effectively stopping them for a second, to keep them in line with Earth’s rotation speed.
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