An Etymological Dictionary of Astronomy and Astrophysics

The dimming of light during its travel in the → interstellar medium due to absorption by → intervening → dust grains. Since shorter wavelengths are particularly affected, the spectrum of the light is increasingly dominated by the long wavelength end of the spectrum. As a result, the light is “reddened” as it travels through space. Robert J. Trumpler (1886-1956), a Swiss-American astronomer,
was the first to produce a definite evidence of the existence of → interstellar extinction and to estimate its magnitude (1930).

See also: → interstellar; → reddening.