Why is the sky blue?

This is due to the scattering of sunlight by air.

Sunlight is broad-spectrum, including infrared, visible and ultraviolet rays. Its energy is concentrated in visible light centered on yellow light. Visible light can be divided into red, orange, yellow, green, cyan, blue, purple and other different colors. These different colors of light combine to produce white vision in our eyes. So the real color of sunlight is white.

Air scatters light passing through it. Some light passing through the air will deviate from the original direction of motion and leave the original beam, and the shorter the wavelength of light (light with short wavelength corresponds to blue light and light with long wavelength corresponds to red light), the greater the scattering effect.

When sunlight passes through the air, blue light scatters more and red light scatters less. This is why the sky is blue. At the same time, this is also the reason why the sun appears red or orange at sunrise or sunset.

Some people may ask that the wavelength of violet light is shorter than that of blue light. Why is the sky blue instead of purple? Although the shorter the wavelength of light, the more scattering. But there are still various wavelengths in scattered light. In other words, the scattered light includes red, orange, yellow, green, cyan, blue, purple and other colors. These rays combine to form a sky-blue vision in our eyes.

The atmosphere itself is colorless. The blue of the sky is a picture created by atmospheric molecules, ice crystals, water droplets and sunlight.

When sunlight enters the atmosphere, long-wavelength colored light, such as red light, has great transmission power and can penetrate the atmosphere and shoot to the ground; However, violet, blue and cyan light with shorter wavelength will easily scatter when it touches atmospheric molecules, ice crystals and water droplets. Scattered purple, blue and cyan light fills the sky, making it appear blue.