An Etymological Dictionary of Astronomy and Astrophysics

A forbidden line emitted by interstellar ionized gas by several atomic species (O, O⁺, O⁺⁺, N⁺, S⁺⁺, etc.) corresponding to the transition from the electronic state 1S to 3P.
Examples are the ultraviolet line of the doubly ionized oxygen
[O III] at 2321 A and [N II] 3063 A. → auroral line;
→ forbidden line; → nebular line.

See also: → trans-; → auroral line.