July 4, 2022
Round, oval, or potato?  What is the true shape of the earth?

Round, oval, or potato? What is the true shape of the earth?

Around 330 BC, the Greek philosopher Aristotle met Evidence Suffice it to claim that the Earth would have a spherical shape. He proved something that Pythagoras had already defended, six centuries before Christ. but will our planet Is it really spherical?

As humanity expanded its knowledge Universe, also expanded his horizons and vision of the universe. With limited vision, limited to human vision at the time, we could only see the horizon as far as our eyes could reach. This horizon was basically flat, therefore, from the point of view of man at that time, our world should be flat.

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But Aristotle was able to see more. Many observed lunar eclipses, and found that the Earth’s shadow cast on the moon It was always circular, no matter where the moon was in the sky. This can only mean that our planet is spherical.

Around 330 B.C., Aristotle concluded that the Earth was spherical by analyzing the shape of the Earth’s shadow cast on the moon during a lunar eclipse. Photo: Jean-Francois Gott

Two centuries later, Eratosthenes of Cyrene achieved another remarkable feat. Using the wand and mathematics, he was able to calculate the circumference of the Earth with an accuracy of only a few kilometers.

Several subsequent studies have confirmed and refined our view of the shape of the Earth. Until the middle of the last century, we finally managed to leave the surface of the planet, and from space we found unequivocally that the Earth is spherical.

Now, if you’re a geographer, you might be a little upset, because you know the Earth isn’t a perfect sphere. In fact, our planet is an amorphous mass, and no matter the terrain, it will have the shape of a geode. And what could a geoid be?

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In short, a geode is the shape our planet would take if it were completely covered by water. Since gravity pulls everything towards the center of the Earth, we can imagine the direction is that this shape would be spherical. But it is not, for two reasons.

First, because the Earth is spinning. The centrifugal force due to the Earth’s rotation is greater near the equator, and this reduces the effect of gravity in this region of the planet, causing the globe to flatten slightly at the poles.

Moreover, the interior of our planet is not a uniform mass. Small differences in the composition and density of the Earth’s crust and mantle lead to subtle changes in the force of gravity at the surface, causing the planet to have an irregular shape. where is the gravity The larger, the distance between the center of the Earth and sea level is less for places where gravity is lower.

Mean ripple of a geoid relative to a reference ellipsoid – Source: Wikimedia

The result of all this is the geoid, which would be the true shape of the Earth had it not been for the rest, making the planet’s surface more uniform. But that doesn’t make Earth a potato-shaped planet as we see in many of the illustrations there.

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Graphics like these are computer generated and have the function of highlighting differences in terrain and gravity at every point on the planet. For this, the technique of vertical exaggeration is used, which makes these differences more noticeable. But, of course, the Earth does not have the shape of a football that resembles that of a dog.

For us to get a good idea of ​​what our planet really looks like, the flatness at the poles is about 0.3%. This makes the Earth’s diameter measured at the poles only 43 km smaller than the 12,756 km at the equator. The difference between this flat ball, which we call the “elliptical of revolution” and the Earth’s geoid, is no more than 16 meters at some points on the surface.

On the left, a false-colored geode ripple with shaded fading and vertical exaggeration (scale factor 10,000). True, the geoid itself ripples in false colors, but at full scale – Source: International Center for Global Earth Models (ICGEM)

Even if we take into account the irregularities of the relief, they are insignificant in relation to the size of the land. For example, Mount Everest at 8,849 meters is less than 0.1% of the diameter of the planet.

Of course, many scientists, especially geologists, need to consider all these small differences in order to achieve more accurate results in their work. But for us and for most people, we can say that our planet is spherical. After all, even given its flatness and differences in gravity and relief, planet Earth is still more perfectly spherical than a snooker ball.

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