An Etymological Dictionary of Astronomy and Astrophysics
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The → polarization arising from line scattering in the presence of "weak" magnetic fields. The effect occurs when precession around magnetic field depolarizes and rotates polarization of the scattered light. The Hanle effect is sensitive to ~10³ times smaller field strengths than the → Zeeman effect. It is in particular used to measure the weak magnetic field of the solar → prominences, which is 10^-3 tesla and over 10^-2 tesla for the active prominences.

Named for the German physicist Wilhelm Hanle (1901-1993), who published his his discovery in 1923 (Naturwissenschaften 11, 690); → effect.