The concept that the earth is spherical can be traced back to the 5th and 6th centuries BC. The Pythagorean philosophers in Greece at that time only produced this concept from the most beautiful spherical concept. Aristotle scientifically demonstrated that the earth is spherical for the first time according to the fact that the shadow on the moon is round during the eclipse. As early as the Warring States Period in China, the philosopher Hui Shi put forward the view that the earth is spherical.
In the 3rd century BC, the ancient Greek geographer Eratosthenes successfully measured the meridian length between Aswan and Alexandria by triangulation.
The concept that the earth is spherical was first put forward by Pythagoras, an ancient Greek philosopher in the 5th and 6th century BC. But his belief is only because he thinks that the sphere is the most perfect of all geometric forms, not based on any objective facts. Later, Aristotle gave the first scientific evidence that the earth was spherical according to the fact that the shadow on the surface of the moon was round during the eclipse. In the 3rd century BC, Eratosthenes, an ancient Greek astronomer, calculated the circumference of the earth for the first time according to the midday sunlight and the distance between two observation points. In 726 AD, a group of astronomers from the Tang Dynasty in China presided over the national astronomical geodesy, and calculated the length of meridian and the circumference of the earth by using the height of the North Pole and the length of summer day. 1622 The global voyage led by Portuguese navigator Ferdinand Magellan proved that the earth is indeed spherical. At the end of 17, Newton studied the influence of the earth's rotation on the shape of the earth, and thought that the earth should be an ellipsoid with slightly convex equator and slightly flat poles. 1733, the Paris Observatory sent two expeditions to carry out geodesy in Peru at 2° S and Lapland at 66 N respectively, and the results proved Newton's conjecture.
After the 1960s, artificial satellites went into the sky, which added a new means for geodesy. According to accurate measurement, the average equatorial radius of the earth is 6378. 14 km, the polar radius is 6356.76 km, the equatorial perimeter and meridian perimeter are 40075 km and 3994 1 km respectively, the height of the North Pole is about 18.9 m, and the height of the South Pole is about 24-3 m.. Some people say that the earth is like a big pear upside down. In fact, these irregular parts of the earth are insignificant to the earth. Judging from the photos of the earth taken by artificial earth satellites, it is more like a standard sphere.