Lyman series

A series of spectral lines in the ultraviolet spectrum of atomic hydrogen, resulting from transitions between the ground state and the various possible excited states. The lines are termed alpha, beta, gamma, and so on, corresponding to transitions to and from the first, second, third, and successive excited states. The Lyman alpha line lies at 121.566 nanometres, the wavelengths of the other lines in the series all being shorter. It is a strong line in the emission spectra of active galactic nuclei and quasars and, if they are at high redshifts, appears shifted into the visible part of the spectrum.