Extinction (astronomy)

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.^[1]^[2] However, its effects had been noted in 1847 by Friedrich Georg Wilhelm von Struve,^[3] 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.^[4]

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.^[5]

^ Trumpler, R. J. (1930). "Preliminary results on the distances, dimensions and space distribution of open star clusters". Lick Observatory Bulletin. 14 (420): 154–188. Bibcode:1930LicOB..14..154T. doi:10.5479/ADS/bib/1930LicOB.14.154T.
^ Karttunen, Hannu (2003). Fundamental astronomy. Springer. p. 289. ISBN 978-3-540-00179-9. {{cite book}}: |work= ignored (help)
^ Struve, F. G. W. 1847, St. Petersburg: Tip. Acad. Imper., 1847; IV, 165 p.; in 8.; DCCC.4.211 [1]
^ Whittet, Douglas C. B. (2003). Dust in the Galactic Environment. Series in Astronomy and Astrophysics (2nd ed.). CRC Press. p. 10. ISBN 978-0750306249.
^ See Binney and Merrifeld, Section 3.7 (1998, ISBN 978-0-691-02565-0), Carroll and Ostlie, Section 12.1 (2007, ISBN 978-0-8053-0402-2), and Kutner (2003, ISBN 978-0-521-52927-3) for applications in astronomy.