Interstellar Absorption

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Interstellar Absorption


the dimming of light during its passage from a radiating celestial body (star, galaxy) through the interstellar medium. It is caused by scattering, diffraction, and absorption of the light by minute particles of cosmic dust (with diameters of the order of 1 μm), which are randomly distributed in interstellar space or concentrated in individual dust nebulae. The amount of interstellar absorption ranges from tenths of a stellar magnitude to several stellar magnitudes per kiloparsec. It is different in different directions because of the unequal distribution of cosmic dust but is particularly significant near the plane of the Milky Way.

Interstellar absorption can be detected by a general weakening in the radiation and a change in the color of stars. Stars whose light has been scattered by the interstellar medium have a noticeably fainter short-wave range, which causes them to appear redder than stars of the same type that are free of interstellar absorption. Interstellar absorption is also observed outside the optical spectrum; this has been confirmed by observations made with telescopes lifted above the earth’s dense atmosphere. The scattering effectiveness and the amount and nature of interstellar absorption depend on the size and nature of the particles in the interstellar medium. Calculation of the interstellar absorption, which distorts the brightness of stars, is very important for the determination of precise distances to stars and for the study of the structure of our galaxy.

The existence of interstellar absorption was first deduced by V. la. Struve in 1847, but its detailed study was begun only in the 1930’s. After the discovery of interstellar absorption, corresponding corrections had to be introduced for distances to stars and galaxies calculated from comparison of the apparent and absolute magnitudes.

When the light of a star is absorbed by clouds of interstellar gas present in the interstellar medium, interstellar absorption lines arise in the star’s spectrum (the majority of these belong to calcium, sodium, and iron and to a number of molecules).

Interstellar absorption can be studied by methods of stellar astronomy involving star counts in selected areas of the sky, by methods using photoelectric multicolor photometry, and by other methods.


Kaplan, S. A., and S. B. Pikel’ner. Mezhzvezdnaia sreda. Moscow, 1963.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
Ehrenfreund, "Detection of two interstellar absorption bands coincident with spectral features of [C.sub.60.sup.+]," Nature, vol.
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Combining this known intrinsic brightness with the newly established distance, and accounting for interstellar absorption, astronomers estimate that the supernova peaked with an apparent brightness between magnitude -7.9 and -7.1.
The astronomers' spectra are of such quality that they are able not only to determine the stars' effective temperatures to very high precision but also to remove the effects of interstellar absorption of starlight, another problem plaguing LMC distances.
For example, it should cope well with the few million faint stars per square degree found in Baade's Window - a corridor of low interstellar absorption toward the galaxy's rich inner regions in Sagittarius.
These are much broader than typical interstellar absorption lines and have been seen in the spectra of many galactic and extragalactic objects.

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