Rayleigh scattering Elastic scattering of light produced by the molecules. The scattered light has the same wavelength as the incident light. The mechanism of Rayleigh scattering is the following. Under the influence of an external electric field, positive and negative charges are displaced forming an electric dipole. The varying electric field will make the dipole oscillate. The oscillating dipoles will emit light, of the same frequency as that of the incident light. Rayleigh showed that the amplitude of scattered light is inversely proportional to the fourth power of wavelength. The intensity of scattered light is given by,

I = I₀ 8 p⁴ N a ² l ^-4 R^-2(1-cos ² q ) (r5)

where I₀ is the intensity of incident light, N the number of molecules, a the polarizability, l the wavelength of incident light, R the distance between the point of observation and the scattering center, and q the angle subtended by the scattered light and the forward direction.

The most important point is that the intensity of the scattered light is inversely proportional to the fourth power of wavelength. Thus light of shorter wavelength is scattered much more than the light of longer wavelength. Indeed the blue region of the solar spectrum is scattered out of the sunlight. Thus the sun appears yellow and sky appears blue.