(ORDO NEWS) — Atomic clocks, combined with precise astronomical measurements, showed that the length of the day suddenly began to increase. This has an impact not only on timekeeping, but also on the technologies that govern our lives.
Over the past few decades, the rotation of the Earth around its axis has accelerated. However, since 2020, this constant acceleration has been replaced by a slowdown. The days are getting longer again, and the reason for this is still a mystery.
For millions of years, the Earth’s rotation has been slowed down by lunar tides. This process increases the length of each day by about 2.3 milliseconds every century.
Over the past 20,000 years, another process has been accelerating the Earth’s rotation. As the last ice age ended, the melting of the polar ice sheets relieved surface pressure and the Earth’s mantle began to move toward the poles.
The rotational speed of our planet increases as the mass of the mantle approaches the Earth’s axis. This process shortens each day by about 0.6 milliseconds every century.
Strong earthquakes can change the length of the day. In addition to these changes, weather and climate also have an important effect on the Earth’s rotation, causing oscillations in both directions.
Tidal cycles, atmospheric movement, ocean currents and groundwater extraction also play a role.
Since the 1960s, when operators of radio telescopes around the planet began to develop methods for simultaneously observing space objects, we have had accurate estimates of the speed of the Earth’s rotation.
Comparison of these estimates with the readings of atomic clocks has shown that the length of the day has been steadily decreasing in recent years.
But, when we take away the rotational fluctuations that occur due to tides and seasonal effects, we can see that even though the Earth reached its shortest day on June 29, 2022, there has been a trend towards longer days since 2020.
The reason for this is not clear. This may be due to changes in weather systems or successive La Niña events.
Scientists have suggested that this is due to the “Chandler wobble” – a slight deviation of the Earth’s axis of rotation with a period of about 430 days. Observations from radio telescopes also show that the wobble has decreased in recent years.
There is also an opinion that these may be long-term tidal effects, working in parallel with other periodic processes and causing a temporary change in the speed of the Earth’s rotation.
An accurate understanding of the Earth’s rotation rate is important for a variety of technologies. If the Earth were to move to even longer days, we might have to include a “negative leap second”, but this is not necessary yet. Now we can be glad that we have a few extra milliseconds every day.
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