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CHILDREN'S SCIENTIFIC LABORATORY
What is the actual shape of the Earth? Children's Science Lab
Directory / Children's Science Lab Members of the French expedition, who arrived in Guiana in 1672, discovered a strange discrepancy in the time readings between pendulum and spring clocks. Near the equator, the hands of pendulum clocks were 2,5 minutes behind. Only fifteen years later, when I. Newton theoretically proved that the shape of the Earth is different from the ball, it became possible to explain this fact. His reasoning boiled down to the following. If we imagine two channels coming out of the center of the Earth to the North Pole and to the equator, and assume that water does not overflow either from the equator to the pole, or vice versa, then both columns of liquid are balanced. Since the centrifugal forces caused by the rotation of the Earth slightly reduce the force of gravity in the equatorial channel, then, having made the appropriate calculation, Newton came to the conclusion that the equatorial radius is 22 km larger than the polar one. From this followed the conclusion: the globe is not a sphere at all, but an ellipsoid. For more than a hundred years, Newton's data remained the most accurate. Then, using astronomical instruments, scientists measured the length of a one-degree parallel at the equator and near the pole. Measurements continued until the middle of our century, when in 1948 the English surveyor G. Jeffrey determined that the discrepancy between the earth's radii was 32,7 km. But this value was not the most accurate.
After the launch of the first satellite, scientists discovered an unexpected deviation of its orbit from the calculated one. When he flew over the equatorial regions, some forces changed the plane of the orbit, and it gradually shifted to the west at a speed of eight degrees per day. This value was measured with high accuracy. And here's what the scientists found. The difference in radii affects the change in the orbit of the satellite in the same way as on a pendulum clock. Thanks to the instruments taken out of the Earth, it was possible to correct the measurements of G. Jeffrey - the difference in radii increased by another 200 m. The last result rather not pleased, but upset the scientists. After all, he did not confirm the results of geodesists, who by that time had carefully measured all the continents with an accuracy of 9 m. It turned out that the model of the Earth - a globe - was incorrect. Or maybe, on the contrary, the results obtained from satellites are incorrect. All this led scientists to think that considering the Earth even as an ellipsoid meant too much simplification of the picture. When studying the acoustic properties of a string, scientists decompose vibrations that are complex in shape into the fundamental tone and sinusoidal harmonics of higher frequencies. The same principle was used to determine the shape of the Earth, but instead of a string, they took an ideal spherical surface. Sequentially, one after another, all harmonics were superimposed on it, which were determined depending on their influence on the satellite's orbit. Here is the first harmonic - zero. It shows a ball whose center of mass is in the equatorial plane. The second harmonic is two-lobe, ellipsoidal. The third is three-petal, resembling a slice of a pear, and so on.
Even harmonics - the second, fourth, sixth, eighth, etc. - have the greatest influence on the change in the orbit in the western direction. To determine them, the satellites were launched at different angles to the equator. Odd harmonics - the third, fifth, seventh, etc. - change the perigee - the distance of the smallest distance of the satellite from the Earth's surface. This occurs mainly when the satellite passes from the northern hemisphere to the southern and, like an electron, "jumps" into a far orbit. By measuring several orbits with different inclinations to the equator, we also managed to determine the values of all odd harmonics. When scientists added up all the harmonics, the model of the Earth turned out to be very complex: mentally cut through the poles, it would look like a slice of a pear with a handle at the North Pole. But the sides of the fetus would not look perfectly even. Elevations and depressions can be found in many parts. In the picture you see how the American scientist M. Kaula represents our planet. On the contour map, contour lines show elevation differences - geoids - the conditional surface of the Earth without its natural relief, over which the waters of the World Ocean are poured. More precisely, the geoid is understood as a surface where the magnitude of the earth's acceleration is always the same. To better understand this complex picture, let's take an imaginary journey on the water surface of the geoid around the equator. Let's start from the point of 20 ° east longitude in Africa to the east. At first we will be at level zero, therefore, at a true distance from the center of the Earth - 6378 km. In order to stay at sea level while crossing the Congo River, we will have to make a tunnel. In the Indian Ocean, we will gradually approach the center of the planet, reaching its greatest dip at 70° East. Here, the center of the Earth is closer by 79 m. In the north of New Guinea, we will have to climb to a height of 67 m. The further path will pass without much descent and ascent, because in the middle of the Pacific Ocean we are floating on a surface with a zero level. Then we will descend 20 m below the level off the coast of South America. And finally, we will return to the starting point from where we started our journey. The constructed picture of the earth's surface, it would seem, completed the work begun by Newton. But scientists continue to look for an answer to the question: how and how to explain the presence of giant elevations and depressions on the surface of our planet? Recently, a new model of the Earth's structure was developed by the Hungarian scientist Academician D. Barta. With precise calculations and observations of the change in the magnetic field, he showed that the earth's core is not located in the center of our planet, but is displaced by 450 km in the direction of Australia. Now take another look at M. Kaul's map. An amazing coincidence - in this part of the earth's surface is also the largest elevation. But there are two more elevations on the map, one in the region of Western Europe, the other between Africa and Antarctica. There are new hypotheses. It is possible that the central core, like the surface of our planet, is not a sphere. Most likely, this giant drop of molten substances, compressed by monstrous pressure, resembles a potato with growths that do not stay in place. Slowly, with almost imperceptible speed, they flow from one edge to the other. And in time with them, elevations and depressions on the surface move, the shape of the earth's crust changes, mountains form.
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