Why the sky is blue?

The sky is blue because of a phenomenon called Rayleigh scattering, where the tiny molecules in Earth’s atmosphere scatter shorter, bluer wavelengths of sunlight more effectively than longer, redder wavelengths. While violet light is scattered even more, the sky appears blue to us because our eyes are more sensitive to blue light and the sun emits slightly more blue than violet light. 

Sunlight composition: White sunlight is made up of all the colors of the rainbow.

Atmospheric scattering: As sunlight enters the atmosphere, it collides with gas molecules like nitrogen and oxygen.

Wavelength and scattering: These molecules scatter shorter wavelengths (blue and violet) much more than longer wavelengths (red and orange).

Color perception: Because blue light is scattered in all directions, the sky looks blue to us from the ground.

Why not violet? Violet light is scattered even more, but there is less violet in sunlight to begin with, and our eyes are simply more sensitive to blue light.

Sunsets: At sunrise and sunset, sunlight travels through more of the atmosphere to reach our eyes. This path scatters away most of the blue and violet light, allowing the less-scattered red and orange light to be visible instead.