Editing Faraday effect (section)

==== Interstellar medium ====
Faraday rotation is an important tool in [[astronomy]] for the measurement of magnetic fields, which can be estimated from rotation measures given a knowledge of the electron number density in the [[interstellar medium]].<ref>{{cite book|last1=Longair|first1=Malcolm | author-link=Malcolm Longair|title=High Energy Astrophysics|publisher=Cambridge University Press|date = 1992|isbn=978-0-521-43584-0 }}</ref> In the case of [[radio pulsar]]s, the [[dispersion (optics)|dispersion]] caused by these electrons results in a time delay between pulses received at different wavelengths, which can be measured in terms of the electron column density, or [[dispersion measure]]. A measurement of both the dispersion measure and the rotation measure therefore yields the weighted mean of the magnetic field along the line of sight.  The same information can be obtained from objects other than pulsars, if the dispersion measure can be estimated based on reasonable guesses about the propagation path length and typical electron densities. In particular, Faraday rotation measurements of polarized radio signals from extragalactic radio sources occulted by the solar corona can be used to estimate both the electron density distribution and the direction and strength of the magnetic field in the coronal plasma.<ref>{{cite journal |last1=Mancuso |first1=S. |last2=Spangler |first2=S. R. |title=Faraday Rotation and Models for the Plasma Structure of the Solar Corona |date=2000 |journal=[[The Astrophysical Journal]] |volume=539 |issue=1 |pages=480–491 |doi=10.1086/309205 |bibcode = 2000ApJ...539..480M |doi-access=free }}</ref>