消光（Extinction）是天文学中观测者用来描述被观测的天体发射的光线被路途中的物质（气体和尘埃）吸收和散射的状态。对地面的观测者而言，消光来自于星际物质（ISM）和地球大气层，他也可能来自于被观测天体周围的星周尘。大气层的消光在一些波段（X射线、紫外线和红外线）上非常强烈，必须进入太空才能观测。在可见光的波段上，蓝色远比红色被稀释的强烈，结果是天体会比预期的偏红，星际消光也会使天体红化 (不要与红移混淆了)。

In astronomy, extinction is the absorption and scattering of electromagnetic radiation by dust and gas between an emitting astronomical object and the observer. Interstellar extinction was first documented as such in 1930 by Robert Julius Trumpler. However, its effects had been noted in 1847 by Friedrich Georg Wilhelm von Struve, and its effect on the colors of stars had been observed by a number of individuals who did not connect it with the general presence of galactic dust. For stars that lie near the plane of the Milky Way and are within a few thousand parsecs of the Earth, extinction in the visual band of frequencies (Photometric system) is on the order of 1.8 magnitudes per kiloparsec.