The blue sky proves the existence of "empty shell"

The atmosphere around us is empty, which is human intuition on the ground.

Looking at the earth from space, the existence of the atmosphere is obvious. The sky seen by astronauts is dark, and the sun and stars shine brightly. Only the earth is beautiful and soft, like a crystal blue agate ball. The dark blue band of light formed by the atmosphere outlines the outline of the earth from the boundless darkness.

Physics tells us that the appearance of this blue sky proves that there is a relatively dense atmosphere here. Because visible light with different wavelengths in the sun will selectively change direction and scatter when encountering particles in space; What color of light is scattered is related to the size of particles and the path through the atmosphere. In pure air with low water vapor and dust content, blue light scatters the most, so what we see is blue sky. If particles larger than air molecules are mixed in, or the path of light passing through the atmosphere becomes longer when the sun is oblique, the light of yellow, orange, red and other colors with longer wavelength than blue light will be scattered, and they will be mixed together, making the sky yellow, white, gray or other colors. In the space near the earth, the atmosphere becomes thinner and thinner. When there are few particles to scatter sunlight, the sky becomes dark. The dense atmosphere is limited in thickness, so the blue band seen by astronauts is only a thin layer.

In fact, the atmosphere above the blue sky is still very thick, but very thin. At the altitude of 100km, the atmospheric density is less than one ten thousandth of the air density on the sea surface, but it has been able to make those meteorites flying to the earth generate high temperature rapidly due to the friction with the atmosphere, and most meteors burn, break and become gas in the atmosphere. This is the meteor we saw.

Ultraviolet rays in solar radiation and high-energy particle streams from the universe will destroy genes that are the basis of life. Fortunately, most of them are intercepted by the atmosphere, otherwise the earth can only be an inanimate world. The atmosphere can be called the shield of life. Because of the existence of the atmosphere, the earth has become the best place to preserve life. Although the crust made of rocks is far stronger than the atmosphere, it will eventually be protected by the atmosphere, otherwise it will have been hit by meteorites, just like on the surface of the moon (Figure 4- 1).

The ancients did not know that the blue or other colors of the sky were the expression of the existence of the atmosphere, and thought that there was an empty world between "heaven" and "earth". In fact, in this blue space, the density of matter is one billion times that of the tail of a comet. We live in dense air, just like fish live underwater.

Figure 4- 1 Moon surface photo (quoted from the latest 20th century children's encyclopedia, 1998)