ATOMIC ABSORPTION SPECTROMETRY (AAS):

Atomic absorption spectrometry (AAS) works by beaming light of a set frequency through a gas flame (acetylene-oxygen, or acetylene-nitrous oxide) into which an aqueous solution of the sample has been vaporized. In this case, the orbital electrons in the flame plasma, absorb certain quanta of light from the beam in order to jump up to higher energy levels. But in the reverse to XRF, a detector opposite the light source measures the intensity of the loss of a particular frequency and the elemental (or oxide composition) computed in relation to a set of known aqueous standards run through the AAS alternately with samples. 

Elements present in the atmosphere of the sun and stars also produce absorption spectra. Numerous dark bands in the spectrum of light emitted by these objects are characteristic of the elements present. The dark bands are specific frequency photons that have been absorbed by the elements in the suns (or stars) atmosphere. Spectral analysis of sunlight is virtually long-distance AAS.