A material's absorption spectrum shows the fraction of incident
electromagnetic radiation absorbed by the material over a range of
frequencies. An absorption spectrum is, in a sense, the opposite of an
emission spectrum. Every
chemical element has absorption lines at several particular
wavelengths corresponding to the differences between the energy levels of its atomic orbitals. For example, an object that absorbs
blue,
green and
yellow light will appear
red when viewed under white light. Absorption spectra can therefore be used to identify elements present in a gas or liquid. This method is used in deducing the presence of elements in
stars and other gaseous objects which cannot be measured directly.
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