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Faraday rotation(fa -ră-day) The rotation of the plane of polarization experienced by a beam of plane-polarized radiation when it passes through a region where there are free electrons and a magnetic field. The plane of polarization is rotated through an angle equal to λ2RM, where λ denotes the radiation wavelength. RM is the rotation measure and is proportional to the integral along the line of sight of the product of the electron density, n e, and the component of the magnetic flux density, B , parallel to the line of sight. Faraday rotation can occur in the interstellar medium, within radio sources themselves, or in the Earth's ionosphere. The interstellar magnetic field can be estimated by dividing the rotation measure by the dispersion measure. The synchrotron emission from a radio source may become depolarized by random Faraday rotation within the source.
Faraday rotation[′far·ə‚dā rō′tā·shən]