Previous Year Question

When white sunlight enters the Earth's atmosphere, it interacts with air molecules and very small particles. Light of shorter wavelength is scattered more strongly than light of longer wavelength.

For Rayleigh scattering, approximately—

Thus, the smaller the wavelength , the greater the scattering.

Blue light has a much shorter wavelength than red light and is therefore scattered much more strongly by atmospheric molecules. This scattered blue light reaches our eyes from different directions, making the sky appear blue.

Dispersion is not the correct phenomenon here. Dispersion refers to the separation of white light into its constituent colours, as in a prism. Interference results from the superposition of coherent light waves.

A useful point is that violet light has an even shorter wavelength than blue and is scattered more strongly. However, the Sun emits comparatively less violet light and the human eye is less sensitive to violet, so the sky appears predominantly blue.