oa MNASSA : Monthly Notes of the Astronomical Society of South Africa - Measuring the brightness of the stars
The first estimates of the brightness of the stars were made with the naked eye. Hipparchus divided all the visible stars into the three classes of bright, medium and faint. This classification was elaborated by Ptolemy who used six classes or 'magnitudes'. He assigned the brightest stars to the first class, the faintest visible to the naked eye to the sixth, and used the letters mu and epsilon to denote whether a star was brighter or fainter than the average of the class to which it was assigned.
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