- noun the splitting of single spectrum lines into two or more polarised ones when the spectrum’s source is put in a magnetic field
- (written as Zeeman Effect)The phenomenon whereby strong magnetic fields cause spectral lines to split into separate components. The Zeeman Effect can be used to determine the strength of stellar magnetic fields. Pieter Zeeman (1865–1943), a Netherlands physicist, discovered the effect in 1896 and it was used early in the 20th century to measure the powerful magnetic fields in sunspots. It began being applied to measurements of other stars in 1946.