Wednesday, August 10, 2022

The length of Earth's days has been increasing, Are we really in danger?

Do not trust posts that present scientific news in a sensational tone and praising mystery or catastrophe.

The only truth is that June 29, 2022 was actually the shortest day (1.59 milliseconds). Have you noticed? Eh), since the 1960s, when we started measuring time with atomic clocks.

Solar time is 86400s (24 hours) almost always, but over the months and years there can be discrepancies. In general, the days are getting longer (0.002s per century!), due to the dissipation of rotational energy due to the tidal interaction of Earth and Moon. In a narrower range we see that the duration of the day fluctuates day by day.

Atomic clocks, very precise (over millions of years), give the measure of time called International Atomic Time (TAI), while the average rotational time of the Earth is measured by Universal Time (UT1). When the difference between UTC (world standard) and UT1 reaches 0.9s by the year, a "leap second" is added to the clocks. So our clocks are accurate with an error of 1 second on the average length of the day.

Because these seconds are added, the difference between TAI (which is constant) and UTC increases by an integer number of seconds, while the difference between UTC and UTC1 is always less than 0.9s.

In 1972 the first "leap second" was added, and UTC was already 10 seconds behind TAI. Since then 27 more seconds have been added, the last one on 31/12/2016. This means that UTC is 37s back on TAI.

If the Earth continues to accelerate you could enter the first negative "leap second", but for many teams there is a 70% chance of being at a minimum and therefore you will not need to take away a second.

Is that black magic? No, it’s physics. The Earth is a very complex and unknown system (especially in the interior), far from simplifying the rigid body.

The cause for changes on a short scale processes in the inner or outer layers, movements of the oceans and/or tides. Another cause could be the "Chandler Wobble", a fluctuation of the geographic pole around the axis of rotation.

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