A limiting feature in a series of absorption lines from a single element (e.g. hydrogen), representing the wavelength at which the element becomes ionized. In the Balmer series of hydrogen, the lines become closer together as the series limit of 364.6 nm is reached, forming an edge at that wavelength (see Balmer Limit). Similarly, in the Lyman series the lines become closer towards the Lyman limit of 91.2 nm.
Subjects: Astronomy and Astrophysics.