Why is the sky blue?

This is because sunlight is composed of seven colors: red, orange, yellow, green, cyan, blue and purple. The wavelengths of these seven colors are different. Compared with other photons with longer wavelengths, dust and other particles in the atmosphere scatter blue light more, so the sky looks blue. The air contains many tiny dust, ice crystals and water droplets. White sunlight is actually composed of seven colors of light: red, orange, yellow, green, cyan, blue and purple. When sunlight shines on the ground through the sky, long-wave rays such as red, orange and yellow can easily penetrate particles and reach the ground, while short-wave rays such as cyan, blue and purple are blocked by micro-roughness suspended in the air and scatter in all directions, making the sky appear blue.

The sky itself is not blue. ...

When sunlight shines into the atmosphere, it will scatter when it meets atmospheric molecules and particles suspended in the atmosphere. Violet, blue and cyan light waves with shorter wavelengths are most easily scattered, while red, orange and yellow light with longer wavelengths have stronger transmission ability. They can pass through atmospheric molecules and particles and keep moving in the original direction, and are rarely scattered by air molecules. For lower air molecules, mainly blue light is scattered and appears in your eyes, so the sky is blue. ?

The blue of the sky can only be seen at low altitude. With the increase of height, as the air becomes thinner and thinner, the number of atmospheric molecules decreases sharply, the light scattered by molecules gradually weakens, and the brightness of the sky becomes darker and darker. At an altitude of more than 20 kilometers, the scattering effect is almost invisible and the sky turns black.