The analysis of spectra, especially light or mass spectra, to determine properties of their source.♦ In light or optical spectroscopy, the spectrum of a light source is analyzed through a spectroscope to determine atomic composition of a substance. In astronomy, phenomena such as red shift can also be analyzed.♦ In mass spectroscopy, a spectroscope is used to determine the composition of ions or charged molecules in a sample. Spectroscopy is also called spectrography. See also atomic spectrum spectroscope.

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