Abstract The Zeeman effect is the splitting of spectral lines into several components by a strong magnetic field. In the normal Zeeman effect, which is shown by atoms without electron spin, each line is split into three. In the more common anomalous Zeeman effect, which is shown by atoms with non-zero spin, the line structure is more complicated. The effect was first observed by the Dutch physicist Pieter Zeeman (1865-1943) in 1896.