Spectroscopy

Spectroscopy is the analytical method of identifying a substance by the specific pattern of wavelengths it emits or absorbs, its spectrum, rather than by its bulk chemical or physical properties directly. Distinct from the spectroscope, the instrument this atlas already carries that splits light into that pattern: spectroscopy is the method of reading and interpreting what the instrument shows. Robert Bunsen and Gustav Kirchhoff established it as a working analytical method in 1859-1860, showing that each chemical element produces its own unmistakable set of spectral lines regardless of what it is burned or combined with, and using it within a year to discover two previously unknown elements, caesium and rubidium, by their spectra alone. Kirchhoff went further, recognising that the dark absorption lines in sunlight, first catalogued decades earlier by Joseph von Fraunhofer without explanation, matched the emission lines of known elements, making it possible to determine what stars are made of from their light alone; the method is now central to chemistry, physics and astronomy alike, though it was first established for chemical analysis.