Caption: A cartoon of a continuous spectrum and emission line spectrum.

Each atom, molecule, and ion has a virtually unique set of lines, and therefore its line spectrum (either emission line spectrum or absorption line spectrum) is virtually its fingerprint. Thus, a line spectrum allows you to identify the species present in a gas.

With the right analysis tools, some other data, and modeling, line spectra will also tell you temperature, density, and composition.

On the other hand, a continuous spectrum tells much less.

If an observed continuous spectrum is at least approximately a blackbody spectrum, it will tell you the temperature of the source by fitting a synthetic blackbody spectrum to it.

Credit/Permission: © David Jeffery, 2003 / Own work.
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