Apparent Magnitudes and Colour Indices of Stars
Hipparchus and many of the earlier astronomers long ago catalogued the brightnesses of stars. We may speak of stellar photometry in the modern sense since N. Pogson in 1850 gave a clear definition of magnitudes and J. C. F. Zöllner in 1861 constructed his visual photometer with which one could accurately compare the bright-ness of a star with that of an artificial starlike image by employing two nicol prisms. (Two such prisms whose planes of polarisation are inclined at angle a to each other reduce the intensity of light passing through them both by a factor cos2 a.)
KeywordsColour Index Sensitivity Function Stellar Atmosphere Apparent Magnitude Photometric System
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