The Earth has recorded its shortest day since the 1960s

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• 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 the Earth clocked 28 of its shortest recorded days. 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.  
• 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.
• 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.  

Factors responsible for days getting shorter-

• Scientists aren’t entirely sure.  They say that something has changed, and changed in a way we haven’t seen since the beginning of precise radio astronomy in the 1970s.
• They 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.
• 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. 
• 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.
• 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 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.
• 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.

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