PrismaA glass prism can split sunlight into a spectrum of all the colours of the rainbow. Optical spectroscopy is the study of this phenomenon: the diffraction of visible light by a prism. Due to the enormous development of spectroscopy during the 19th century we know today what the sun and other stars are made of, and how atoms are constructed.

In 1814 the German optician Joseph von Fraunhofer constructed an instrument to measure the diffraction of light when it passes through glass – the spectroscope. He observed the presence of dark lines in the diffracted sunlight and eventually identified almost 600 of these so-called spectral lines.

Spectral lines

Researchers soon discovered that there are spectral lines in light coming from other sources, not just in sunlight, and that these lines have different characteristics.

The sun’s atmosphere can be investigated
The German researchers Gustav Kirchoff and Robert Bunsen were able to show that different spectral lines are associated with different elements. An element not only emits, but also absorbs, light with a particular wavelength. It is thus possible to identify the elements in a solid or gas, just by analysing its spectrum.
This technique was used by Anders Ångström in 1862 to determine that the sun’s atmosphere is composed of hydrogen and several other elements. He also published a solar atlas, a detailed survey of the sun’s spectrum.
At the end of the nineteenth century researchers made spectroscopic analyses of light from many different sources, ranging from elements in laboratory test tubes to far-distant stars.

Joseph von Fraunhofer (1787–1826) constructs the first spectroscope and discovers spectral lines.
Léon Focault (1819–1868) and Anders Ångström discover, independently of each other, that elements both emit and absorb light of the same wavelength.
Gustav Kirchoff (1824–1887) and Robert Bunsen (1811–1899) demostrate that each element has characteristic spectral lines.
Anders Ångström (1814–1874) conducts a detailed survey of the solar spectrum, Recherches sur le spectre solaire.