DISCOVERY OF THE MONTH
Discovery of helium in Fraunhofer line in the solar spectrum – October 20, 1868
Fraunhofer lines are a set of spectral lines named after the German physicist Joseph von Fraunhofer (1787–1826). The lines were originally observed as dark features (absorption lines) in the optical spectrum of the Sun. When light passes through material and is absorbed by atoms and ions of each element (hydrogen, calcium, sodium, iron etc.) a unique set of dark lines is formed in the spectrum.