scattering

scattering

1. the random deflections suffered by light or other electromagnetic radiation passing through an irregular medium. If the source, medium, or observer are in relative motion, scintillations – random fluctuations of amplitude – may be seen as the source is observed through the medium: scattering in the Earth's atmosphere causes the stars to twinkle. Scintillations may only be seen if both the angular size of the source and the bandwidth in which the waves are received are small enough. Otherwise, the effect of the scattering may simply be to broaden the apparent angular size of the source.

Scintillations of radio waves are observed to occur because of irregularities in the refractive index of the ionosphere, the interplanetary medium, and the interstellar medium giving ionospheric scintillation, interplanetary scintillation (IPS), and interstellar scintillation (ISS), respectively. IPS may be used in determining the angular sizes of radio sources at meter wavelengths in the range 0.1 to 2 arc seconds, or for measuring parameters of the solar wind. ISS cause some of the random fluctuations in the intensity of pulses received from pulsars.

Light may be deflected from its direction of travel by fine particles of solid, gaseous, or liquid matter. For very small particles (less than one wavelength in size) the effect results from diffraction, reflection playing a more important part with increasing size; this is known as Rayleigh scattering and is very dependent on wavelength. Very small particles scatter blue light more strongly than red light. This leads to the reddening of starlight by cosmic dust and to the reddening of the Sun when seen through a thick layer of atmospheric dust.

2. the deflection of individual particles (such as electrons or photons) from their direction of travel as a result of their interaction with other particles, nuclei, atoms, or molecules in the medium through which they are passing. There are various scattering processes including Compton scattering.

Collins Dictionary of Astronomy © Market House Books Ltd, 2006

scattering

[′skad·ə·riŋ]

(electromagnetism)

Diffusion of electromagnetic waves in a random manner by air masses in the upper atmosphere, permitting long-range reception, as in scatter propagation. Also known as radio scattering.

(physics)

The change in direction of a particle or photon because of a collision with another particle or a system.

Diffusion of acoustic or electromagnetic waves caused by inhomogeneity or anisotropy of the transmitting medium.

In general, causing a collection of entities to assume a less orderly arrangement.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.