The Earth is round
It is interesting that, as early as 2,000 years ago, even though there were no satellites or modern technology, people knew that the Earth was spherical.
It was the Greeks who believed that the Earth was spherical before they had any proof. The eminent mathematician and philosopher Pythagoras was the first to hypothesize that the Earth was spherical in 500 BC. Pythagoras believed that, in his eyes, the sphere was the most perfect shape.
Since BC, many people have believed that the Earth is spherical. (Photo: Sohu)
A century later, the philosopher Plato offered a similar opinion. However, the person who actually proceeded to prove that the Earth was spherical was the Greek philosopher – Aristotle. He gave some evidence in his book “On the Heavens” written in 350 BC. According to Aristotle, we can only see the Earth’s shadow on the Moon during lunar eclipses. It is always spherical no matter where the Earth is on its rotation.
In another argument, he suggested that the positions of the stars would be different when we looked at them in different places on Earth. For example, the stars in Egypt cannot be seen in Cyprus 1,000 km away. This proves that the Earth is not only round but also a sphere.
In Europe, the ancients also consciously believed that the Earth was spherical. In particular, after the explorer Ferdinand Magellan’s ship circumnavigated the Earth, many people believed in the existence of the spherical Earth theory.
How to know the Earth is spherical?
Many people think that using shoreline observations can prove that the Earth is spherical. But scientists say this method cannot observe the contour of the Earth’s circle.
Even using a telescope to observe the ocean, you will not be able to prove the above point. Because if you use a telescope you can clearly see the coastline of the ocean, if you use it on the ground you will see a horizon line. However, no matter where you stand, you are standing on an arc of the Earth, visibility will be limited, the degree of curvature of the Earth is different and the distance between the arcs is also different.
Our earth is not everywhere flat or bare, so it is very difficult to verify that the surfaces are curved. (Photo: Sohu)
This limitation of arcs can only prove that the Earth has a curved surface, but cannot show whether it is curved elsewhere.
Our earth is not everywhere in plains or bare land, in addition, there are mountainous terrains and plateaus, so it is difficult to verify that the surfaces are curved. Similarly, scientists also said that people even standing on the top of the world’s highest mountain like Everest still cannot see the whole Earth.
How far away from Earth does it take to see it as spherical?
When sitting on the plane, we can see the mountains and the ground below in a flat, square form. Typical aircraft altitude is between 7,000 and 12,000 meters. But according to what the human eye sees when traveling on an airplane, this altitude still cannot clearly see the spherical Earth. Because the Earth is so large, for a sphere with a radius of more than 6,000 km, an aircraft flying at an altitude of 10,000 meters cannot see the whole scene.
So what does the earth look like to astronauts in space?
Neil Armstrong saw the Earth perfectly spherical while standing on the Moon. (Photo: Sohu)
According to the description of many astronauts, when at an altitude of 118 km above sea level, they saw a light blue star in their vision. This altitude can be considered as the boundary between Earth and space. Beyond this height, it is clear that in the human eye the Earth can be seen as a sphere.
American astronaut – Neil Armstrong once said that, when he stood on the Moon, he saw the Earth completely and was stunned by the scene before him.
In fact, at 1,000 kilometers above the Earth’s surface, astronauts can see the larger arc of the Earth’s edge when they look out of windows. If you increase the altitude to 2,000 km, at this distance, the astronaut can clearly see the arc of the Earth. And of course, at a distance of about 400 km from the Earth’s surface like the International Space Station, astronauts can easily see the spherical Earth most clearly.
Source: ASU, Sohu