Why the sky is blue when we see it?

Explanation

The amount of scattering is inversely proportional to the fourth power of the wavelength. This is known as Rayleigh scattering.
The bluish colour predominates in a clear sky since blue has a shorter wavelength than red and is scattered much more strongly.
In fact, violet gets scattered even more than blue, having a shorter wavelength.
But since our eyes are more sensitive to blue than violet, we see the sky blue.