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A process in which all or part of a beam of electromagnetic radiation or particles is deflected from its initial direction of travel, without any absorption or emission. Light is scattered by fine particles, such as dust, through the mechanism of reflection or diffraction (or both). If the particles are smaller than the wavelength of the light, the effect is purely one of diffraction and the phenomenon is known as Rayleigh scattering. The intensity of scattered light, as viewed from any particular direction, varies with wavelength l as 1/l4. This means that blue light is scattered more effectively than red. The daytime sky is blue because the blue component of sunlight is scattered by air molecules, while the rising or setting Sun, viewed through a thick layer of atmosphere near the horizon, is red because blue light is removed by scattering from the rays being observed directly. The same phenomenon produces interstellar reddening. Scattering may also be caused by direct interaction between a beam of radiation and the nuclei or electrons in the material through which it is passing. See also: Compton effect. |