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Friday, August 12, 2022

Explained: The Earth has recorded its shortest day since the 1960s — why are we spinning faster, and what impact can it have?

On June 29, the Earth completed one full spin — a day — in 1.59 milliseconds less than its routine 24 hours.

Written by Raghu Malhotra , Edited by Explained Desk | New Delhi |
Updated: August 6, 2022 8:38:45 am
On July 26, the day ended 1.50 milliseconds earlier, with the Earth almost breaking the record it set on June 29.(Illustrative/Pixabay)

Time flies, goes the idiom, and on recent evidence this seems to be true — literally. Tomorrow is often coming sooner these days — albeit by a fraction of a second. On June 29, the Earth completed one full spin — a day — in 1.59 milliseconds less than its routine 24 hours. It was the shortest day recorded since the 1960s, when scientists first began to use the precise atomic clocks to measure the Earth’s rotational speed.

It’s been happening fairly often these days — in recent years, the Earth has been spinning ever so slightly faster. On July 26, the day ended 1.50 milliseconds earlier, with the Earth almost breaking the record it set on June 29. And in the year 2020, when all that the world could think about was the coronavirus, the Earth clocked 28 of its shortest recorded days, the website timeanddate.com reported. July 19 was the shortest of these short days of 2020 — ending 1.47 milliseconds sooner.

A millisecond is one-thousandth of a second. For perspective, the average blink of an eye lasts a tenth of a second, that is, for 100 milliseconds. And P T Usha missed the bronze medal at the 1984 Olympics in Los Angeles by one-hundredth of a second. (Usha clocked 55.42 seconds in the 400 metre hurdles; bronze medallist Cristieana Cojocaru of Romania finished in 55.41 seconds. And No. 5 Ann-Louise Skoglund of Sweden clocked 55.43.)

So, the Earth is in a hurry. Is this new?

Not really. While the Earth has been completing its rotations faster in recent years, when looked at over a much longer period of time, our planet is actually spinning slower.

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Every century, the Earth takes a few milliseconds longer to complete one rotation — and on average, days are actually getting longer. So, 1.4 billion years ago, a day would have ended in less than 19 hours, The Guardian reported  in 2018, quoting a scientific paper published that year. The paper attributed the larger trend of the Earth’s slower spin mostly to the gravitational pull of the Moon, which causes tidal friction and slows down the Earth’s rotations.

Then why are days getting shorter these days?

Scientists aren’t entirely sure. “It’s certainly odd,” Professor Matt King of the University of Tasmania told ABC News. “Clearly something has changed, and changed in a way we haven’t seen since the beginning of precise radio astronomy in the 1970s.”

He hypothesized that climate change-induced surface variations, which impact the way that the Earth spins, could be a reason. These surface variations include melting ice sheets in Greenland and Antarctica, as well as changes in ocean circulation.

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“We don’t know the cause of the acceleration of Earth’s rotation. We have only hypothesis…,” Christian Bizouard of the Paris Observatory at the International Astronomical Union told the Chinese television network CGTN. “We assume that the cause is internal and lies in the movement of Earth’s core,” he said.

Among the many processes that affect the speed of the Earth are movements in the planet’s inner molten core, seismic activity, wind speed, and shifting atmospheric gases, The Guardian said in a separate report published this week. Activities that push mass towards the centre of the Earth will hasten the planet’s rotation, while anything that pushes mass outwards will slow down the spin, the report noted.

Some experts suggest that the shortened length of the day could be related to the ‘Chandler wobble’, a phenomenon that refers to the small deviation in the movement of Earth’s geographical poles. According to Dr Leonid Zotov of the Sternberg Astronomical Institute of Lomonosov Moscow State University, this wobble has recently diminished and could be the reason behind shorter days. “The normal amplitude of the Chandler wobble is about three to four metres at Earth’s surface, but from 2017 to 2020 it disappeared,” Dr Zotov told timeanddate.com.

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According to NASA, “the spinning Earth is affected by many factors, including changes in the way the winds blow or currents in the ocean. Some of these factors can act to speed the planet up, while others literally drag it down.”

What can happen if the Earth continues to spin faster on a sustained basis?

To ensure that the time on clocks matches the speed of the Earth’s rotation, a system of leap seconds has been used since the 1970s. They involve one-second adjustments to Coordinated Universal Time (UTC), the time standard used to synchronize clocks around the world. Due to the long-term slowing in the planet’s spin, 27 leap seconds have been added to UTC.

However, if the Earth continues to spin faster and days subsequently become shorter, scientists may have to introduce the first ever ‘negative leap second,’ which involves a subtraction of a second from clocks.

A blog post published on July 25 on Meta Engineering argued that while leap seconds benefit scientists and astronomers, it “is a major source of pain for people who manage hardware infrastructures”. The authors of the post claimed that an addition of a leap second had caused the website Reddit to be inaccessible for 30 to 40 minutes in 2012, and since a negative leap second has never been tested on a large scale, “it could have a devastating effect on the software relying on timers or schedulers”.

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First published on: 04-08-2022 at 06:45:23 pm
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