This lithographic reproduction of the spectrum of the sun is about three feet long, and was published by Lerebours et Secretan of Paris. The lines across the spectrum represent the Fraunhofer lines due to absorption. The first observation of these lines was made by William Hyde Wollaston (1766-1828), who saw seven of them. Joseph Fraunhofer (1787-1826) independently discovered the two closely-spaced sodium absorption lines in light from various sources, and then observed it in sunlight. There he discovered an "almost countless number" of lines, which have come to be known by his name.

    The upper curve represents the response of the human eye. Note that the spectrum extends into the infrared and ultraviolet regions.

   Observing the spectrum of the sun was often done by using a heliostat to direct the light of the sun toward a spectrometer.