Rayleigh scattering refers primarily to the elastic scattering of light from atomic and molecular particles whose diameter is much smaller (one-tenth at least) than the wavelength of the incident light. The amount of scattering is strongly depending on the wavelength (λ) of the radiation (I = f(1/λ4). Then, the Rayleigh scattering explain the blue color of the sky caused by the scattering of sunlight off the molecules of the atmosphere. This because Rayleigh scattering is more effective at short wavelengths (the blue end of the visible spectrum). Therefore the light scattered down to the earth at a large angle with respect to the direction of the sun's light is predominantly in the blue end of the spectrum.