interstellar extinctionThe reduction in brightness, i.e. the extinction, of light (and other radiation) from stars as a result of absorption and scattering of the radiation by interstellar dust. Although dust makes up only a small proportion of the interstellar medium, its effect on starlight is considerable. The amount of extinction, usually measured in magnitudes, depends on the direction of observation. It is a maximum (about one magnitude per kiloparsec distance for visible wavelengths) toward the center of the Galaxy, where the density and extent of the dust is greatest. The extinction varies inversely with wavelength. Red light is thus less affected than blue light so that starlight appears reddened when observed through a dust cloud; this interstellar reddening can also be used to map the presence of dust in the Galaxy. Radio and infrared waves with their longer wavelengths can pass through the interstellar medium with ease compared with optical wavelengths. The presence of obscuring matter between the stars was first conclusively demonstrated by Robert Trumpler in 1930.
interstellar extinction[¦in·tər¦stel·ər ik′stiŋk·shən]
The dimming of light from stars due to its absorption and scattering by dust grains in the interstellar medium.