Extinction (astronomy)
in astronomy, the absorption and scattering of electromagnetic radiation by dust and gas between an emitting astronomical object and the observer
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 lying near the plane of the Milky Way which are within a few thousand parsecs of the Earth, extinction in the visual band of frequencies (photometric system) is roughly 1.8 magnitudes per kiloparsec.
For Earth-bound observers, extinction arises both from the interstellar medium and the Earth's atmosphere; it may also arise from circumstellar dust around an observed object. Strong extinction in Earth's atmosphere of some wavelength regions (such as X-ray, ultraviolet, and infrared) is overcome by the use of space-based observatories. Since blue light is much more strongly attenuated than red light, extinction causes objects to appear redder than expected; this phenomenon is called interstellar reddening.
Interstellar reddening
Interstellar reddening is a phenomenon associated with interstellar extinction where the spectrum of electromagnetic radiation from a radiation source changes characteristics from that which the object originally emitted. Reddening occurs due to the light scattering off dust and other matter in the interstellar medium. Interstellar reddening is a different phenomenon from redshift, which is the proportional frequency shifts of spectra without distortion.
The public source identifies “Extinction (astronomy)” as in astronomy, the absorption and scattering of electromagnetic radiation by dust and gas between an emitting astronomical object and the observer. This brief keeps that definition visible, then builds a research path around Extinction, astronomy and absorption.
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The date and method of observation matter as much as the stated conclusion, especially where classification or consensus has changed. The source revision retrieved here is dated Aug 23, 2026. The linked authority identifier is Q943247. The first chronological checks are 1930 and 1847.
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