Rayleigh Scattering

Rayleigh scattering is the scattering of light or other electromagnetic radiation by particles much smaller than its wavelength; for light below the resonance frequency of the scattering medium, the amount of scattering is inversely proportional to the fourth power of the wavelength. It arises because the oscillating electric field of a light wave sets charges within a small particle vibrating at the same frequency, and the particle then re-radiates that light in most directions like a small dipole, a process most pronounced in gases. In the atmosphere of Earth, Rayleigh scattering of sunlight is why the daytime sky looks blue, because shorter blue wavelengths scatter far more strongly than longer red wavelengths and so arrive at the eye from all directions; at sunrise and sunset, blue light has been scattered out of the direct path to the observer, leaving mostly yellow, orange, and red light visible toward the sun. The phenomenon is named for the British physicist Lord Rayleigh, John William Strutt.