<P> The Zeeman effect (/ ˈzeɪmən /; Dutch pronunciation: (ˈzeːmɑn)), named after the Dutch physicist Pieter Zeeman, is the effect of splitting a spectral line into several components in the presence of a static magnetic field . It is analogous to the Stark effect, the splitting of a spectral line into several components in the presence of an electric field . Also similar to the Stark effect, transitions between different components have, in general, different intensities, with some being entirely forbidden (in the dipole approximation), as governed by the selection rules . </P> <P> Since the distance between the Zeeman sub-levels is a function of magnetic field strength, this effect can be used to measure magnetic field strength, e.g. that of the Sun and other stars or in laboratory plasmas . The Zeeman effect is very important in applications such as nuclear magnetic resonance spectroscopy, electron spin resonance spectroscopy, magnetic resonance imaging (MRI) and Mössbauer spectroscopy . It may also be utilized to improve accuracy in atomic absorption spectroscopy . A theory about the magnetic sense of birds assumes that a protein in the retina is changed due to the Zeeman effect . </P>

According to the zeeman effect the splitting of a sunspot's spectral lines is due to