Abstract
I.—APPARENT MAGNITUDES: (a) VISUAL.THE magnitude of a star, as determined by direct astronomical observation, is a measure of its apparent brightness on a scale which has been precisely defined only within recent years. Hipparchus was, so far as is known, the first to assign magnitudes to the stars, and his results have been preserved for us by Ptolemy in the Almagest. The classification of Hipparchus was a crude one, the stars being divided into six classes, all the brightest stars being assigned to the ist magnitude, and all those only just visible to the naked eye to the 6th. Ptolemy extended the classification by recognising the gradation in brightness between the stars in a given class, this gradation being indicated by the words and used to denote that a star was brighter or fainter than the average star of its class. Ptolemy's estimations were adopted almost universally until the time of Sir William Herschel, who developed a plan for representing various degrees of difference in brightness between stars by the use of arbitrary symbols, and made observations of the magnitudes of nearly three thousand stars. It was not until Argelander carried out the great project of the “Bonn Durch-musterung” (1852 onwards) that magnitudes were first estimated to tenths, and even in this great work the scale adopted, though made to correspond fairly closely with the then existing scales, was an arbitrary, and not a uniform, one.
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JONES, H. Stellar Magnitudes and their Determination. Nature 107, 142–146 (1921). https://doi.org/10.1038/107142a0
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DOI: https://doi.org/10.1038/107142a0