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The dimming of light from distant stars by absorption and scattering by interstellar dust. The effect decreases with increasing wavelength. Extinction is less effective for red light than for blue, resulting in the phenomenon of interstellar reddening. The blue light from a star near the centre of the Galaxy is reduced in brightness by 25 magnitudes by the interstellar material along our line of sight. At infrared and radio wavelengths, which are longer than those of visible light, the interstellar medium is increasingly transparent. In the ultraviolet, extinction continues to increase towards shorter wavelengths; it has been studied down to 100 nanometres.
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