Hydrogen and Helium Emissions

There is now a wealth of observational data on the emission lines of H seen in the atmosphere. The α and β lines of the solar Lyman series at 1216 and 1026 A excite the extensive H in the terrestrial atmosphere causing it to re-emit them; they are then seen from space above the absorbing lower atmosphere. Scattering of the solar Ly-β line by the atmospheric H also produces the Balmer series Hα line (6563 A) seen from the ground. The interpretation of early Ly-α observations has been summarized (Mange, 1972); discussion is limited here to contributions from 1970 on. Auroral H emission and its excitation are neglected.