Earth breaks record for shortest day

Science | Astronomy

Since 2020, the shortest 28 days of all those measured since the 1960s have been recorded

Earth is in a hurry. Or so it seems. On average, our planet takes 24 hours to complete one rotation with respect to the Sun, that is, 86,400 seconds. However, the Earth's rotation is not constant, so most days are a little longer or a little shorter than that. What has scientists surprised is that the Earth has been stringing together many shorter-than-normal days in recent years.

In 2020, the shortest 28 days were recorded since atomic clocks began to be used to measure the speed of the Earth's rotation in 1960. In 2022, it has already broken its best mark twice. On July 26, the day lasted 1.50 milliseconds less (1 millisecond is equal to 0.001 seconds); while the shortest day ever recorded occurred just a month earlier, on June 29, when the Earth took 1.59 milliseconds less to complete its rotation.

The causes of this mysterious terrestrial acceleration are not yet clear. Scientists are considering hypotheses that point to geological processes in the internal or external layers of the Earth, such as the action of the oceans, the tides or even the climate, but nothing is certain and the investigations continue, as collected by the specialized portal on time timeanddate.com.

For their part, Russian researchers Leonid Zotov, Christian Bizouard and Nikolay Sidorenkov, from Lomonosov University, have suggested at the annual meeting of the Asia-Oceania Society for Geosciences that the current decrease in day length could have some relation to the 'Chandler wobble', a small deviation of the Earth's axis. Meanwhile, other experts maintain that it could be due to the fact that the Earth is slightly elliptical, to seismic activity or to the imbalance of the weight of the poles due to melting.

A negative leap second

If we take long periods as a reference, the Earth's spin is slowing down. If we take long periods as a reference, the Earth's spin is slowing down. The effect of the moon on our planet is the main cause of it. Therefore, every century, our planet takes a couple of milliseconds longer to complete one rotation. 1.4 billion years ago, for example, the day lasted less than 19 hours. To compensate for that shift and keep clocks aligned with the planet's spin, the International Earth Rotation and Reference Systems Service (IERS) adds occasional leap seconds. That is, they stop the clocks for a second so that the Earth can catch up to its rhythm. The first leap second was added in 1972 and the last one on December 31, 2016.

If the rapid rotation of the Earth continues, the day may come when we must introduce the first negative leap second. This means that we would have to steal a second from our clocks so that they can keep up with the accelerating spin of the planet. It sounds simple, but this could create problems for a variety of technologies, such as GPS, smartphones, computers, and communications systems. Still, Zotov thinks there's a 70% chance that won't be necessary.