Day length in planet it suddenly seems to us that it is getting larger, as accurate atomic clocks and astronomical observations show, but scientists are not yet sure why this is happening. An increase in the day, even if imperceptible, by fractions of a second, may in the future affect, among other things, timekeeping, navigation systems such as GPS and other technologies.

In recent decades, the rotation of the Earth around its axis, which determines the length of the day, has accelerated, as a result of which the days have become shorter. So this year in June, the record for the shortest day in the last half century was recorded.

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

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

Over millions of years, the rotation of the Earth slowed down, mainly due to the tides under the influence of the Moon, and this process added about 2.3 milliseconds to the length of the day every century. Billions of years ago, an Earth 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, accelerating the rotation of our planet. When the last ice age ended, their melting “lightened” the surface of the Earth, and its axis began to rotate 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 rotational speed. In combination with a personal watch that offers the highest accuracy, an increasing reduction in the length of the day has been confirmed.

The shortest day

On June 29, 2022, the shortest day on Earth was recorded: 1.59 milliseconds short of 86,400 seconds or 86,400,000 milliseconds of the normal 24-hour period. But if you take into account and remove the fluctuations associated with tides and seasonality, it seems that from 2020 to the present, imperceptibly begins to lengthen again.

The reason for this – to the extent that it actually occurs – is unclear. This is likely due to changing weather systems, increased ice melt due to climate change, natural disasters such as the massive volcanic eruption in Tonga in January of this year, etc. The phenomenon may be transient, which remains to be seen in the future.

If it is eventually confirmed that the days on Earth are getting longer again, perhaps, according to Matt King and Christopher Watson of the Australian University of Tasmania, at some point a “negative leap second” will have to be built into the timing systems, which is not happening. This happened again, which, however, is currently considered very unlikely. Let’s just consider that lately we all have a few extra milliseconds every day…

Source: APE/MEB