The blue colour of the sky is due to the scattering of sunlight by the molecules of the atmosphere. According to Rayleigh’s law of scattering, the intensity of scattered light, I ∝ 1/λ4 blue colour having the short wavelength in the visible spectrum scatter the most. When we look at the sky, the scattered light enters our eyes and this light contains blue colour in a large proportion, so the sky appears blue.
