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I wonder if you have ever thought about this question when you were a child: Why are the earth, sun and moon round? When we want to draw the sky on paper or computer, we will naturally draw a circle.
When I grew up, as I learned more about astronomy, I discovered that all celestial bodies in the universe are round. Not only the earth, the moon and the sun, but also all the planets, stars and satellites that we already know are round.
What is the reason that allows the entire universe to be so "uniformly" showing the same shape?
The magical law of universal gravitation
The planet is round, which is related to the law of universal gravitation.
We are all familiar with the law of gravity. We have all read the story of " Newton and Apple " since childhood. Newton's thought about why apples fall downwards when they are ripe prompted him to think, why do objects go downwards instead of in other directions?
The famous scientist Newton proposed the law of universal gravitation in the 17th century, which was later hailed as one of mankind's greatest scientific achievements. It had a profound impact on subsequent scientific development, with the greatest impact on astronomy and physics.
The law of universal gravitation can reveal the laws of celestial bodies in the universe and provide methods for astronomical calculations. The discovery of the following famous planets is evidence that the law of universal gravitation is applied to astronomy.
Contemporary astronomical scientists follow the formula proposed by Newton and based on the current astronomical observation data, they can calculate the trajectory of these stars in the universe.
Of course, the emergence of any theory and technology is not achieved overnight. The relevant conjectures about universal gravitation were actually born in the famous philosopher Aristotle in ancient Greece. They were later supplemented by sages in ancient Greece. After generations of philosophers, mathematicians, and physicists, they continued to improve, and finally we have the law of universal gravitation that we currently understand.
Because of the existence of this law in the universe, it governs the movement of various planets and celestial bodies. For example, satellites revolve around stars, which is the reason for the universal gravitation between satellites and stars.
In fact, any object, when its gravity reaches balance, will become a circle, which is a very stable state.
Therefore, all the stars we know will follow this rule and show a very stable spherical shape.
However, the law of universal gravitation is not considered to be able to explain everything. Many of Newton's theories were later proven to be incomplete.
In the past many years, people have relied too much on the formulas proposed by Newton, using formulas to calculate and solve problems, but for a long time no one has really paid attention to the nature of "mechanics" and the original meaning of these formulas.
Of course, there are also a group of scientists who are tirelessly exploring this related field and striving for the truth.
For example, the universe later described in Einstein's theory of relativity is different from the universe in Newtonian mechanics which is widely recognized.
From Einstein's point of view, gravity in the theory of relativity is more like geometry than a single mechanics. Gravity can be regarded as a kind of "space-time curvature" energy, and any object has energy.
Einstein’s understanding of the universe from the perspective of relativity is very different from the universe from the perspective of Newtonian mechanics.
However, Einstein’s theory of relativity also has many physical and astronomical phenomena that cannot be explained for the time being, but this does not affect the conclusion that our planet and most celestial bodies are spherical.
How to prove that the earth is round?
Nowadays, due to the development of science and technology, everyone believes that the earth is round, and there are many image data sent back from the universe to confirm it.
Do you know? Prior to this, humans had paid a lot of money and even sacrificed their lives in order to prove that the earth was round.
In fact, even today, there are still believers in the "Flat Earth Theory" in the Western scientific community who insist that the earth is not round.
In fact, as early as the ancient Greek period, famous geographers came to the conclusion that the earth should be round from the "shadow phenomenon". In the culture of ancient Greece, circle and sphere are both perfect nouns, so of course the earth we live on is also perfect. There were even ancient Greek mathematicians who tried to calculate the diameter of the earth, and the error was not very large.
But in any era, those who violate the widely recognized doctrines of the time will be looked at with suspicion, especially in the era of religious rule, and even one disagreement will be executed.
In the 16th century, Spain ushered in the Age of Discovery, and many maritime explorers appeared, including the well-known Magellan.
Magellan led his fleet and went through hardships for three years to return to Spain. Many sailors were sacrificed during this process, but it was also the first time that he used practical actions to reveal to people the truth that the earth is round.
In fact, by the time of Magellan, most people believed that the earth was round, otherwise the Spanish royal family would not have taken such a big risk to invest in Magellan's fleet.
In several works of Zhang Heng of the Han Dynasty, he repeatedly mentioned that the earth is round like a pellet, and even speculated on gravity and geological structure.
It is said that according to the excavated tombs of the Tang Dynasty, there are already foreign gold coins with the "earth" element in them. However, in that era, cultural exchanges between China and foreign countries were already very frequent, and it was already accepted that the earth is round and we are just a place on the earth.
In fact, we still have many simple ways to prove that the earth is round, such as:
1. You can take a telescope to the port to see the ship going away.
The ship going away is not getting smaller and smaller, but gradually disappears on the ground plane. Of course, when the ship comes back, it also gradually appears on the ground plane.
2. Observing the starry sky
This is also a method used by many ancient sages. Aristotle began to observe different constellations, but the starry sky seen in different dimensions must be different. For example, the ancient Chinese liked to observe the " Big Dipper ". You know, this cannot be seen just anywhere.
If the sky and the earth are flat, then the starry sky observed in different areas should be the same.
Of course, the scientific knowledge of both physics and astronomy is vast. Even these scientists who have been recorded in history can only explore a few things in their lifetimes. Far from being able to explain it clearly in a few articles or a few sentences, if you want to know more, more efforts will be needed from future generations.
