Zeeman effect

The spectral lines of mercury vapor lamp at wavelength 546.1 nm, showing anomalous Zeeman effect. (A) Without magnetic field. (B) With magnetic field, spectral lines split as transverse Zeeman effect. (C) With magnetic field, split as longitudinal Zeeman effect. The spectral lines were obtained using a Fabry–Pérot interferometer. Zeeman splitting of the 5s level of Rb, including fine structure and hyperfine structure splitting. Here F = J + I, where I is the nuclear spin (for Rb, I =  3⁄2). This animation shows what happens as a sunspot (or starspot) forms and the magnetic field increases in strength. The light emerging from the spot starts to demonstrate the Zeeman effect. The dark spectra lines in the spectrum of the emitted light split into three components and the strength of the circular polarisation in parts of the spectrum increases significantly. This polarization effect is a powerful tool for astronomers to detect and measure stellar magnetic fields.

The Zeeman effect ( Dutch: [ˈzeːmɑn]) is the splitting of a spectral line into several components in the presence of a static magnetic field. It is caused by the interaction of the magnetic field with the magnetic moments of the atomic electrons associated with their orbital motion and spin; this interaction shifts some orbital energies more than others, resulting in the split spectrum.