Earth records the shortest day in its history

Earth’s average rotation speed decreases slightly over time – UniversalImagesGroup/Getty Images Contributor

If you feel like there’s never enough time in the day, there may be a reason.

Earth experienced its shortest day since records began last month, with 1.59 milliseconds shaved off the usual 24-hour spin on June 29, raising the possibility that a negative leap second may soon be needed for clocks match the heavens.

In general, the Earth’s average rotational speed decreases slightly over time. Timekeepers have been forced to add 27 leap seconds to atomic time since the 1970s as the planet slows down.

But since 2020, the phenomenon has been reversed: speed records were frequently broken in the last two years.

The previous fastest day was -1.47 milliseconds over 24 hours on July 19, 2020. It nearly broke again on July 26, when the day was -1.50 milliseconds shorter.

While the effect is too small for humans to notice, it can build up over time, which could affect modern satellite navigation and communication systems that rely on time to be consistent with conventional positions of the Sun, Moon and the stars.

It means that it will soon be necessary to remove time, add a negative leap second, and speed up global clocks for the first time.

The ‘Chandler Wobble’

Scientists have been left scratching their heads over the cause, although experts have suggested that a phenomenon known as the “Chadler Wobble” may be having an impact.

Earth’s rotational speed is constantly changing due to the complex motion of its molten core, oceans, and atmosphere, as well as the effect of celestial bodies such as the Moon.

Tidal friction and the changing distance between the Earth and the Moon cause the speed of the planet’s rotation on its axis to vary daily.

“Chandler Wobble” is the change in the Earth’s spin on its axis and normally causes the Earth’s rotation to increase, meaning it takes longer to complete one spin. But in recent years the spin has become less wobbly.

Dr Leonid Zotov of the Sternberg Astronomical Institute at Lomonosov Moscow State University believes this lack of oscillation may be behind the faster days and will present the theory next week at the Asian Society of Geosciences annual meeting. and Oceania.

“The normal amplitude of the Chandler Wobble is about three to four meters at the Earth’s surface, but from 2017 to 2020 it disappeared,” Dr. Leonid Zotov told the Timeanddate website.

In the early 2000s, the amplitude of the “Chadler Wobble” began to decrease and in 2017-2020 it reached an all-time low just as the length of the day began to shorten.

Global warming is a small contributing factor

Other factors that may have an impact on the annual variation include the accumulation of snow on the mountains of the northern hemisphere in winter and then the melting in summer.

Global warming is also expected to have an effect by melting ice and snow at higher elevations, causing the Earth to spin faster, but this is considered to be a relatively small contribution.

Changes in the length of a standard day were only discovered after highly accurate atomic clocks were developed in the 1960s and compared to fixed stars in the sky.

The last leap second was added on New Year’s Eve in 2016, when clocks around the world stopped for a second to allow Earth’s rotation to catch up.

BT’s Talking Clock then added a one-second pause before its third beep, while BBC Radio 4 inserted an additional beep into its 1am bulletin.

The Paris-based International Earth Rotation Service monitors the planet’s rotation and informs countries when leap seconds should be added or removed six months in advance.

However, the leap second could be abolished altogether next year, when the World Radiocommunication Conference decides whether it depends entirely on atomic time.

Britain opposes the move because it would break the link with solar time forever.

Some experts believe that the need for a negative leap second could increase the pressure to move to atomic time.

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