Interstellar extinction

(astronomy) The dimming of light from stars due to its absorption and scattering by dust grains in the interstellar medium.

Dimming of light from the stars due to absorption and scattering by grains of dust in the interstellar medium. In the absorption process the radiation disappears and is converted into heat energy in the interstellar dust grains. In the scattering process the direction of the radiation is altered. Interstellar extinction produces a dimming of the light from stars situated beyond interstellar clouds of dust. Measures of the radiation from pairs of stars of similar intrinsic properties but with differing amounts of interstellar extinction can be used to obtain information about the dependence of extinction on wavelength, which can then be used to provide clues about the nature of the interstellar dust grains. See also Scattering of electromagnetic radiation.

A detailed interpretation of this dependence and other data relating to interstellar dust suggests that the interstellar grains of dust range in size from about 0.01 to 1 μm and are composed of silicate grains and probably some type of carbon grain, and that the interstellar dust acquires coatings of water ice and ammonia ice in the densest regions of interstellar space. A comparison of interstellar extinction with the absorption by interstellar atomic hydrogen reveals that the dust contains about 1% of the mass of the interstellar medium. See also Interstellar matter.