May 21

Blown by the wind, by the waves, and by the Moon, the Earth’s rotation slows down, the number of hours in a day increases with time

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Lessons of tens, hundreds of thousands of years after this time will be even longer.

If you have the opportunity to visit the Cenozoic Era that took place about 620 million years ago, you will see many different things in both space and time. The creature that ruled the Earth’s surface had a strange shape, and the passage of time was nothing like modern times. Because the Earth’s axis rotates faster than it is today, a day hundreds of millions of years ago lasted only 22 hours.

Over billions of years, the Earth’s rotation slows down; This is a process that has been going on throughout history and is still happening. Scientists estimate that each century, a day will grow by about 1.8 milliseconds. The length of a day varies from year to year.

Although the Palm is still spinning, science still doesn’t really understand the factors that influence this pole dance. But with extremely sensitive research instruments, the researchers had near-precise data and tracked the Earth’s rotation time to the micro-second precision.

The result: we learn that the rotation of the Blue Planet is constantly changing, not every day is the same.

So what’s a day?

From the very first day of the founding of the country, the Earth has turned. Any celestial body is formed from matter being pulled together by the influence of gravity, so the rotation is natural. However, this motion is not consistent throughout the existence of the object. The forces that affect the rotation of a celestial body are closely related to the behavior of the core, as well as the direction of air movement (if any) on the surface of the object. That is not to mention the influence from the gravity of other celestial bodies.

Solar system, illustration

Today, science can measure even the smallest changes in the Earth’s rotation thanks to Very Long Baseline Interferometry. Based on space telescopes located far from the ground, and since they observe signals affecting the Earth from space, scientists can observe the rotation by measuring the input and output signals.

Comparing the time between the appearance and disappearance of the signal, we can calculate very accurately the time it takes for the Earth to complete one revolution.

Many factors affect the rotation of the Earth, and the biggest factor, the longest influence is the Moon – man-made satellite. For billions of years, gravity radiating from the Moon slowed the Earth’s rotation. Because of the Moon, a day of the Cenozoic Era lasted only 22 hours, and later on, the number of hours in a day will be even more.

Basically, this mechanism is the transfer of energy between the Earth and the Moon. The gravity of “Sister Hang” causes the rocks on the Earth’s surface to rise slightly, but will not rise at the point directly below the Moon. The difference between the position of the rocky outcrop and the Moon creates a torque, which slows the Earth’s rotation. This rotation force acting on the Moon makes Hang’s mansion fly further and further away from us, at a distance of 3.8 cm/year. However, this is not constant, it varies continuously.

Interactions between the two bodies have been around since the Moon began to orbit the Earth. According to some scientists’ estimates, a day 1.4 billion years ago was only 18.7 hours long. And then, the Moon was located about 43,000 km closer to the Earth than today.

Will tomorrow be longer than today?

Considering an easier time frame to imagine, various factors affect the Earth’s rotation rate. Among them, the one that has the most influence is the Earth’s core. The oscillations of the liquid in the core cause the planet’s rotation rate to change, although it is not clear how large those effects are. We have not yet observed the Earth’s core closely, nor do we know how it affects global activity.

On the surface, wind and wave motion also affect the Earth’s rotational speed. Waves crashing on the shore, wind blowing on the mountainside all have certain effects.

Geological activity also causes the Earth to rotate quickly or slowly. The 2004 earthquake that devastated countries near the Indian Ocean caused the Earth to rotate approximately 3 microseconds faster. The change in Earth’s mass after the earthquake caused the rotation to change. Today, we still have to take into account that the ice melts, the sea level rises, making the poles lighter but the equator heavier; Climate change has caused the Earth to “stagnate”, making the day longer.

And the Earth’s rotational speed also changes with the seasons: faster in the Northern Hemisphere in summer, slightly slower in winter. We fly in an elliptical orbit around the Sun, and when we’re near the fireball, we’re flying faster which means we’re spinning slower.

Just like everything, change is inevitable. However, with changes that are only measured in milli, micro units like Earth’s rotation or crush’s feelings, you don’t need to worry too much about them but just live carefree. A day in the Cenozoic Era may last only 22 hours, but based on what we know, time is still relative.


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