Scientists have lost it: The length of days on Earth seems to be getting longer again

THE during the day on our planet suddenly seems to gets bigger, as precision atomic clocks and astronomical observations show, but scientists aren’t yet sure why this happens. The increase of the day, even imperceptibly, by fractions of a second, may in the future have, among other things, impact on punctualityin navigation systems such as GPS and other technologies.

During the last decades the rotation of the Earth around its axis -which determines how long the day lasts- had accelerated, which made the days shorter in length. So this year in June a record for the shortest day was recorded in the last half century.

But despite this record, since 2020 it seems that the fastest rotation of the planet’s axis has strangely begun to slow down, resulting in a tendency for the days to grow longer again, for reasons that currently remain a mystery.

Altough a day is conventionally defined as having 24 hours, actually the length of “24 hours” varies, depending on how long it takes the Earth to make one full rotation. Which in turn depends on various factors, including events such as a major earthquake, climate and atmospheric phenomena, oceans, etc. Thus, in practice the day rarely lasts 86,400 seconds.

For millions of years the Earth’s rotation had been slowing down, mainly due to the tides under the influence of the Moon, a process that every century added about 2.3 milliseconds to the length of the day. Billions of years ago the Earth’s day lasted no more than 19 hours.

But over the past 20,000 years or so, another process has taken place in the opposite direction, speeding up the rotation of our planet. When the last ice age ended, their melting “lightened” the Earth’s surface and its axis began to spin faster, shortening the length of the day by about 0.6 milliseconds per century.

Since the 1960s scientists have begun to make increasingly precise measurements of the Earth’s rotation speed. Coupled with individual clocks providing the highest precision, the ever-greater reduction in the length of the day was confirmed.

At June 29, 2022 was recorded as the shortest day on Earth: 1.59 milliseconds less than the 86,400 seconds or 86,400,000 milliseconds of a regular 24-hour period. But if the fluctuations due to tides and seasonality are taken into account and removed, it seems that from 2020 to the present day imperceptibly begins to grow longer again.

The reason for this – to the extent that it actually occurs – is unclear. It is probably due to changes in weather systems, the increasing melting of ice due to climate change, natural disasters such as the massive eruption of the volcano in Tonga in January this year, etc. The phenomenon may turn out to be transient, something that remains to be seen in the future.

If it is eventually confirmed that Earth’s days are getting longer again, perhaps, according to Matt King and Christopher Watson of Australia’s University of Tasmania, a “negative leap second” would have to be built into timekeeping systems at some point, something that doesn’t has happened again and which, however, is considered very unlikely at the moment. Let’s just consider that lately we all have a few extra milliseconds each day…

RES-EMP

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