German physicist Gustav Robert Kirchoff (1824–1887), working with chemist Robert Bunsen (1811–1899), best known for his Bunsen burner, helped describe how spectroscopy could be used to identify elements. Each kind of atom or molecule interacts with light to produce its own distinct pattern of colors, much the same way that each kind of item in a supermarket can be identified by its own unique bar code. Kirchoff showed that, if light shines through gaseous matter, then the atoms and molecules in that gas would absorb light if the gas were relatively cool, and emit light if the gas were quite hot. Spectroscopic measurements of distant light sources would thus reveal the patterns of dark “absorption lines” and bright “emission lines” produced by the gas. This would in turn reveal the kinds of atoms and molecules in the gas, as well as their environmental conditions. Kirchoff’s laws of spectroscopy form the foundation of the analysis of light from distant objects.

Kirchoff measured and studied the spectra of a large number of elements and compounds in his laboratory. He also studied the spectra of stars. Building on Kirchoff’s work, British astronomer William Huggins (1824–1910) used photographic technology to record the spectra from very faint and distant stars, opening new avenues of astronomical study. Huggins is known today as the “father” of stellar spectroscopy.