The collection of wavelengths missing from a continuous distribution of wavelengths. Caused by the absorption of certain wavelengths by the atoms or molecules in a gas.
Absorption spectra are unique for each element and compound and they are often used as chemical fingerprints in analytical chemistry. The spectrum can represented by a plot of either absorbance or transmittance versus wavelength, frequency, or wavenumber.
It was unrecognised absorption lines in interstellar spectra that were identified as due to a previously unknown allotrope of carbon. This spherical shell molecule of 60 atoms was named Buckminster Fullerine and later found on Earth.