A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identify atoms and molecules. These "fingerprints" can be compared to the previously collected "fingerprints" of atoms[1] and molecules,[2] and are thus used to identify the atomic and molecular components of stars and planets, which would otherwise be impossible.
Continuous spectrum
Absorption lines (discrete spectrum)
Absorption lines for air, under indirect illumination, with the direct light source not visible, so that the gas is not directly between source and detector. Here, Fraunhofer lines in sunlight and Rayleigh scattering of this sunlight is the "source." This is the spectrum of a blue sky somewhat close to the horizon, pointing east at around 3 or 4 pm (i.e., Sun toward the west[clarification needed]) on a clear day.
https://en.wikipedia.org/wiki/Spectral_line
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