A sharp dip in intensity over a narrow wavelength range in a continuous spectrum. In a spectrum produced by a typical spectrograph, in which the light passes through a narrow slit before being dispersed, absorption lines have the appearance of dark lines cutting across at right angles to the direction of dispersion. Absorption lines are a characteristic of the spectra of the majority of stars. In the case of the Sun, they are known as Fraunhofer lines. Atoms are able to absorb radiation at a number of precise wavelengths. The wavelengths at which absorption occurs are different for each chemical element, making it possible to identify the elements present in a star, or other celestial body, by analysing which spectral lines are present. The strength of the lines can be used to deduce the abundance of the elements, though not directly since the temperature, density and other physical circumstances greatly influence the strength of absorption lines in a spectrum. See also: emission line.