I saw an article the other day that, unsurprisingly, made me curious. The gist of it was that 2020 was the shortest accurately measured day ever and 2021 will be even a bit shorter, with the difference being about a second compared to when accurate measurements began in the 70’s…and oh, nothing to worry about.
Perhaps I shouldn’t have seen this change as the entrance to an exciting rabbit hole into which I’d never before ventured, but alas, I had to check it out, because from what I know, the earth should slow down over time, not speed up. I looked up the accurate measurements (here) and made a graph of the results shown above. The vertical access is the length of the average day in excess of the standard 24 hours.
A few things jumped out at me…first, the length of the day is definitely dropping over time and second, there seems to be some regularity to the wiggle. Now, I am seriously curious.
The length of the day consistently dropping means that the earth is spinning faster and that takes lots and lots of energy — where does it come from? The prevailing wisdom is that the spin of planets is left over from the formation of the solar system, which, if true, would mean that the rate of spin should just slowly decrease over time. More on this later.
The wiggle looks like an oscillation at a regular rate with some little glitch noise — the period of oscillation is around twenty-two years, which happens to be the approximate duration of the cycle of the sun’s magnetic field oscillation. Why and how could that be related, I wondered? It turns out this has been observed by researchers and a variety of relationships have been postulated, but with no conclusions as to a mechanism. That is…yep, but no idea why or how.
I did discover that the length of a particular day has been found to relate to earthquakes. And, a paper in Nature, established that earthquakes are correlated to solar activity — remember the sun sends not only light but also solar wind. This brings us back again to a mechanism…solar wind (electrically charged particles) from the sun interacts with the earth and, apparently, causes changes in the length of the day. How exactly, isn’t clear.
Is it feedback to the earth’s magnetic field? Does solar activity influence the friction between the crust and the mantle? If this is the case, does it mean that there is a big difference between the rotation rate inside the earth? Scientists think the rotation speeds at different depths are not very different, but the truth is that no one really knows what is going on inside the earth, nor what produces the magnetic field. So all we really know is the data in the graph above.
The bible, and legends from other ancient cultures (Toltec for example), describe days where the sun stood still in the sky, or that the length of the day was miraculously extended. As rational scientists, we mostly discount these descriptions, but maybe it isn’t impossible…but if it were possible, the result would be the oceans sweeping across the land, raging winds and other assorted devastations. At the equator, the earth’s surface is moving at around 1000 miles per hour, so if the surface of the earth radically changes rotation speed, the inertia from the deceleration could be catastrophic.
Back to the first question…what about the increase in rotation speed? As mentioned above, scientists say that rotation comes from the initial formation of the solar system, and the moon creates some drag on the earth, and that the spin rate is therefore slowly dropping over millions of years. But, remember, the graph is the only thing we actually know…it isn’t theory, it is real measurement. It says the spin rate is increasing, at an average rate of about one second every fifty years. If this continued, it would mean that in around 4 million years the earth would be going twice as fast as it is now.
I wondered how much energy was involved. It turns out the energy of the earth’s rotation is enormous, and the increase in energy because of the shorter day is over 100 times greater than the total global energy usage over the last fifty years. At least that proves it isn’t anthropogenic spin acceleration. But where the energy is coming from is quite a mystery. The solar wind doesn’t seem to pack that kind of punch.
How can it be that some incredible energy source impacts the earth, is modulated by the sun and we know nothing about it?
There is no sunshine in this rabbit hole. It is very dark, I am confused and I feel a bit trapped.
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