A dark feature in the spectrum of a star, formed by cooler gas in the star's outer layers (the photosphere) that absorbs radiation emitted by hotter gas below. The Fraunhofer lines in the solar spectrum are the best-known examples. Each line is a unique signature of the element or molecule that forms it, which enables the chemical composition of the star to be determined. See also Band.
Subjects: Astronomy and Astrophysics.