If it feels like there’s never enough time in the day, there may be a reason.
Earth experienced its shortest day on record last month, slacking 1.59 milliseconds from its usual 24-hour rotation on June 29 – raising the prospect that a negative leap second may soon be needed to reset the clocks to align with heaven.
Normally, the Earth’s average rotation speed decreases slightly over time. Timekeepers have been forced to add 27 leap seconds to atomic time since the 1970s as the planet slows.
But since 2020, the phenomenon has reversed — with speed records frequently being broken in the past two years.
The fastest day so far was -1.47 milliseconds under 24 hours on July 19, 2020. On July 26, when the day was -1.50 milliseconds shorter, it was almost broken again.
Although the effect is too small for humans to notice, it can accumulate over time – potentially having implications for modern satellite communications and navigation systems that rely on time to track the conventional positions of the Sun, Moon, and Sun and stars match.
This means that it may soon be necessary to remove time, add a negative leap second, and speed up global clocks for the first time ever.
The “Chandler Wobble”
Scientists have puzzled over the cause, although experts have suspected a phenomenon known as the “Chandler Wobble” could be having an impact.
The Earth’s rotational speed is constantly varying due to the complex motion of its molten core, oceans and atmosphere, and the action of celestial bodies such as the moon.
The friction of the tides and the changing distance between the Earth and the Moon cause daily fluctuations in the speed at which the planet rotates on its axis.
The “Chandler Wobble” is the change in the Earth’s rotation about its axis and usually causes the Earth’s rotation to increase, meaning it takes longer to complete a rotation. But in recent years the spin has become less wobbly.
dr Leonid Zotov of Lomonosov Moscow State University’s Sternberg Astronomical Institute believes this lack of fluctuation may be behind the faster days and will present the theory at next week’s annual meeting of the Asia Oceania Geosciences Society.
“The normal amplitude of the Chandler Wobble is about 3 to 4 meters at the surface, but from 2017 to 2020 it disappeared,” said Dr. Leonid Zotov’s site Timeanddate.
In the early 2000s, the amplitude of the “Chandler Wobble” began to decrease, reaching a historic minimum in 2017-20, just as the length of the day was getting shorter.
Global warming is a small factor
Other factors that can affect annual variations include snow that accumulates on northern hemisphere mountains in winter and then melts in summer.
Global warming is also expected to have an impact by melting ice and snow at higher elevations, causing the Earth to spin faster, but it is thought to be a relatively small contribution.
Changes in the length of a standard day were only discovered after highly accurate atomic clocks were developed and compared to fixed stars in the sky in the 1960s.
The final leap second was added on New Year’s Eve 2016 when clocks around the world stopped for a second to allow the Earth’s rotation to catch up.
Then BT’s talking clock added a one-second pause before its third pip, while BBC Radio 4 added an extra pip to its 1am bulletin.
The International Earth Rotation Service, based in Paris, monitors the planet’s rotation and notifies countries six months in advance if leap seconds need to be added or removed.
However, the leap second could be eliminated altogether next year when the World Radio Conference will decide whether to rely entirely on atomic time.
Britain opposes the move because it would sever ties with solar time forever.
Some experts believe the need for a negative leap second could add pressure to move to atomic time.
https://www.telegraph.co.uk/news/2022/07/31/earth-records-shortest-day-ever/ Earth records its shortest day ever