The Zeeman Effect
The magnetic field of the Sun can be probed in a rather precise and direct
manner because in the presence of a magnetic field the energy levels of atoms
(and ions and molecules) are split into more than one level
by the
Zeeman effect.
As discussed in the chapter on the interaction of light and matter,
we can infer the presence of magnetic fields if we observe Zeeman
splitting in the spectrum. Further, we can measure the strength of the field by
measuring quantitatively the amount of Zeeman splitting.