Earth records its shortest day ever

Earth records its shortest day ever

Earth records its shortest day ever

The average rotational speed of the Earth decreases slightly over time - Contributor UniversalImagesGroup / Getty Images

The average rotational speed of the Earth decreases slightly over time – Contributor UniversalImagesGroup / Getty Images

If there never seems to be enough time during the day, there may be a reason.

Earth experienced its shortest day since record-breaking last month, with 1.59 milliseconds shorter than its usual 24-hour turnaround on June 29, raising the prospect that it may soon take a negative leap second to maintain clocks aligned with the sky.

Usually, the average rotational speed of the Earth 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 reversed, with speed records often beaten in the last two years.

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

Although the effect is too small for humans to notice, it can build up over time, with a potential impact on modern time-based satellite navigation and communication systems that is consistent with conventional positions of the Sun, Moon and stars.

It means that time may soon need to be removed, adding a negative leap second and speeding up global clocks for the first time ever.

The “swing of the Chandler”

Scientists are left scratching their heads over the cause, although experts have suggested that a phenomenon known as “Chandler Wobble” could have an impact.

The rotation speed of the Earth varies constantly due to the complex motion of its molten core, oceans and atmosphere, as well as the effect of celestial bodies such as the Moon.

The friction of the tides and the change in distance between the Earth and the Moon determine daily variations in the speed of rotation of the planet on its axis.

The “Chandler Wobble” is the change in the rotation of the Earth on its axis and normally causes the Earth’s rotation to increase, which means it takes longer to complete one revolution. But in recent years, the rotation has become less shaky.

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

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

In the early 2000s, the amplitude of the “Chandler Wobble” began to decline and in 2017-20 it hit an all-time low just as the length of the day began to shorten.

Global warming is a small contributing factor

Other factors that can impact annual variation include snow formation on Northern Hemisphere mountains in the winter and melting in the summer.

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

The standard day-length changes were only discovered after the development of highly accurate atomic clocks in the 1960s and compared to the fixed stars in the sky.

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

Then, BT’s voice clock added a one-second pause before its third pip, while BBC Radio 4 put an extra pip in its 1am bulletin.

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

However, leap second could be abolished altogether next year, when the World Radiocommunication Conference decides whether to fully rely on atomic time.

Great Britain is against the move because it would forever sever the link with solar time.

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

Leave a Reply

Your email address will not be published.