Polarization in astronomy 1614609 199706495 2008-03-20T23:25:22Z Bjweeks 321557 clean up using [[Project:AutoWikiBrowser|AWB]] [[Polarization]] is an important phenomenon in [[astronomy]]. The polarization of [[starlight]] was first observed by the [[astronomer]]s [[William Hiltner]] and [[John S. Hall]] in [[1949]]. Subsequently, [[Jesse Greenstein]] and [[Leverett Davis, Jr.]] developed theories allowing the use of polarization data to trace [[interstellar magnetic field]]s. Although the [[thermal radiation]] of [[star]]s in not appreciably polarized at source, its scattering by [[interstellar dust]] imposes polarization on starlight over long distances. Circular polarization of light from the Sun has, however, been measured; it is due to transmission and absorption effects in strongly magnetic regions of the Sun's surface. Plane polarization of starlight generated at the star itself is also observed for [[Ap star]]s (peculiar A type stars) [http://www.edpsciences.org/articles/eas/abs/2003/04/eas0928/eas0928.html] Polarization is also present in radiation from [[coherent radiation|coherent]] astronomical sources (e.g. hydroxyl or methanol [[Astrophysical maser|masers]]), and incoherent sources such as the large radio lobes in [[Active galaxy| active galaxies]], and [[pulsar]] radio radiation (which may, it is speculated, sometimes be coherent). Apart from providing information on sources of radiation and scattering, polarization also probes the interstellar [[magnetic field]] in our Galaxy as well as in radio galaxies via [[Faraday rotation]]. In some cases it can be difficult to determine how much of the Faraday rotation is in the external source and how much is local to our own Galaxy, but in many cases it is possible to find another distant source nearby in the sky; thus by comparing the candidate source and the reference source, the results can be untangled. The polarization of the [[cosmic microwave background radiation|cosmic microwave background]] is also being used to study the physics of the very early universe. == See also == * [[Reflection polarization]]<!-- This article hasn't been written yet --> * [[Transmission polarization]]<!-- This article hasn't been written yet --> == External links == * [http://www.planck.fr/article263.html Discovery by Hiltner and Hall, analysis by Greenstein] [[Category:Polarization]] [[Category:Astrophysics]] {{astronomy-stub}}