What is "rayleigh scattering"

Rayleigh scattering (pronounced ), named after the British physicist Lord Rayleigh (John William Strutt),Lord Rayleigh (John Strutt) refined his theory of scattering in a series of papers that were issued over a period of decades. Here is a partial list of those papers:

1. John Strutt (1871) "On the light from the sky, its polarization and colour," Philosophical Magazine, series 4, vol.41, pages 107–120, 274–279.
2. John Strutt (1871) "On the scattering of light by small particles," Philosophical Magazine, series 4, vol. 41, pages 447–454.
3. John Strutt (1881) "On the electromagnetic theory of light," Philosophical Magazine, series 5, vol. 12, pages 81–101.
4. John Strutt (1899) "On the transmission of light through an atmosphere containing small particles in suspension, and on the origin of the blue of the sky," Philosophical Magazine, series 5, vol. 47, pages 375–394.

is the (dominantly) elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation. Rayleigh scattering does not change the state of material, hence it is a parametric process. The particles may be individual atoms or molecules. It can occur when light travels through transparent solids and liquids, but is most prominently seen in gases. Rayleigh scattering results from the electric polarizability of the particles. The oscillating electric field of a light wave acts on the charges within a particle, causing them to move at the same frequency. The particle therefore becomes a small radiating dipole whose radiation we see as scattered light.

Rayleigh scattering of sunlight in the atmosphere causes diffuse sky radiation, which is the reason for the blue color of the sky and the yellow tone of the sun itself.

Rayleigh scattering of molecular nitrogen and oxygen in the atmosphere includes elastic scattering as well as the inelastic contribution from rotational Raman scattering in air, since the changes in wavenumber of the scattered photon are typically smaller than 50 cm. This can lead to changes in the rotational state of the molecules. Furthermore, the inelastic contribution has the same wavelengths dependency as the elastic part.

Scattering by particles similar to, or larger than, the wavelength of light is typically treated by the Mie theory, the discrete dipole approximation and other computational techniques. Rayleigh scattering applies to particles that are small with respect to wavelengths of light, and that are optically "soft" (i.e. with a refractive index close to 1). On the other hand, Anomalous Diffraction Theory applies to optically soft but larger particles.