Spectroscopy was discovered in 1859 by Gustav Robert Kirchhoff and Robert Wilhelm Bunsen. German scientist and inventor Joseph Von Fraunhofer observed in the early 1800s that the continuous spectrum was marred by over 700 dark lines (now called Fraunhofer lines). Bunsen and Kirchoff made a prism-based device that separated the visible light emitted. When substances were vaporized into Bunsen's flame, each gas had its own signature spectrum consisting of different Fraunhofer lines.
No body knew what caused these lines until later work by Kirchhoff. Kirchhoff had explained the Sun's Fraunhofer lines -the dark lines in the solar spectrum (the light from the Sun) were the same as the emission lines observed by various heated chemical substances. Kirchhoff realized that the Sun was hot and gaseous, yet what was the cause of these dark lines at the atomic level?