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image of Frauhofer-Lines

Fraunhofer lines, (C) Wikipedia

Spectral absorption lines of the spectrum of the sun, named after the German physicist Joseph von Fraunhofer (1787–1826)
Such Lines are produced whenever a cold gas is between a broad spectrum photon source and the detector.
Photons are absorbed and then re-emitted in random new directions. Therefore the intensity in the original direction is lower and a dark line appears in the spectrum.

wavelength in nm Fraunhopfer line Lightsource color
365.0146 i Hg UV
404.6561 h Hg violet
435.8343 g Hg blue
479.9914 F' Cd blue
486.1327 F H blue
546.0740 e Hg green
587.5618 d He yellow
589.2938 D Na yellow
643.8469 C' Cd red
656.2725 C H red
706.5188 r He red
768.2 A' K red
852.11 s Cs IR
1013.98 t Hg IR

See also Abbe-number, dispersion.