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![Hertzsprung-Russell diagram](http://upload.wikimedia.org/wikipedia/commons/thumb/6/67/HR-diag-no-text-2.svg/350px-HR-diag-no-text-2.svg.png)
Photo credit: NASA/TRACE
In astronomy, stellar classification is a classification of stars based on their spectral characteristics. The spectral class of a star is a designated class of a star describing the ionization of its chromosphere, what atomic excitations are most prominent in the light, giving an objective measure of the temperature in this chromosphere.