An Etymological Dictionary of Astronomy and Astrophysics

A unit of energy used in atomic physics, equal to about 13.6 electron-volts, the ionization potential of hydrogen.

See also: In honor of the Swedish physicist Johannes Robert Rydberg (1854-1919), who did important contributions on spectroscopy, and in particular found a relatively simple expression relating the various lines in the spectra of chemical elements (1890).