Joannes Marcus Marci, who explained the origin of the rainbow on the basis of light diffraction and scattering in water droplets, first observed that sunlight plays an important role in atomic spectrometry in 1648. In 1672, Sir Isaac Newton reported that sunlight passing through a prism was divided into various colors. New developments were reported only in the early 1800s, when William Hyde Wollaston (1802) and Joseph Ritter von Fraunhofer (1814) observed solar radiation dispersion and discovered dark lines in the solar spectrum. Fraunhofer designated the letters A to K to the strongest lines – the best-known line is the sodium D line present in the visible spectrum yellow region (Figure 3.1). In 1836, Sir David Brewster verified that the absorption process in the sun atmosphere caused these lines.^1,2