Rayleigh scattering is the scattering of light by particles that are small in relation to the wavelength of the light. Rayleigh scattering of short wavelengths in sunlight by gas molecules in the atmosphere is the reason the sky appears blue. The phenomenon is named after the English physicist Lord Rayleigh (1842–1919).
In Rayleigh scattering, the amount of scattering (d) is inversely proportional to the fourth power of the wavelength (λ). Thus blue light is scattered by small particles ten times as much as red light.