How did Kirchhoff's work on spectra impact physics?
My investigations into the spectra emitted by heated substances, particularly my formulation of the relationship between emission and absorption spectra, were of paramount importance. I demonstrated that the characteristic spectral lines of an element are both emitted and absorbed at the same wavelengths. This principle, that a cool gas absorbs light at precisely the wavelengths it would emit if heated, provided a powerful tool for identifying the chemical composition of distant stars and understanding the fundamental interactions of light and matter.
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