Do you know what shape the earth is? Many people will blurt out: spherical, of course. This is common sense that adults and children all know. However, human ancestors did not know that the earth was spherical at first. For example, ancient Indians once believed that the earth was a big round shield, which was held up by three elephants standing on the back of a tortoise.
As far back as the early stage of human society, Chinese ancestors had a simple view of heaven and earth, forming the famous theory of "round sky and place" that "the sky is like a cover and the place is like a chess game". In the 6th century BC, Pythagoras, an ancient Greek mathematician, first put forward the "earth circle theory". When observing the lunar eclipse, he found that the projection of the earth on the moon was round, so he thought the earth was a complete sphere. He first put forward the concept of "Earth" and believed that the sphere in the universe was the most perfect. By about 350 BC, Aristotle, another ancient Greek scholar, put forward many powerful arguments for the "earth circle theory": from the port, no matter which direction the ship sails, its hull always disappears from the sea first; The phase change of the moon shows the shape of the earth; People who travel long distances north and South will notice that some stars can be seen in the south that cannot be seen in the north. And he infers that the earth is not only spherical, but also its diameter will not be too large. In the 2nd century AD, another ancient Greek scientist Ptolemy also put forward the view that the earth was spherical in his astronomy.
In September 1519, the Portuguese navigator Magellan was dispatched by the Spanish royal family and led a huge long-distance fleet of 256 people to sail westward from Spain for three years. In September 1522, the fleet returned to Spain and proved indisputably that the earth was round with the first round the world voyage in human history.
More than 100 years later, when studying the centrifugal force of the earth's rotation, Newton calculated that the flatness of the two poles was about 1 / 230 of that of the earth. In other words, the earth is a flat ellipsoid, the equatorial part bulges outward, and the polar regions are flat rather than a standard sphere.
Today, with the development of Aerospace Science and technology, people can accurately observe the shape of the earth from space. In the vast universe, the beautiful blue ellipsoid with a slightly longer East-West radius and a slightly shorter north-south radius is the earth we were born on.