Abstract
RELATION OF SPECTRAL TYPE TO MAGNITUDE.—The Henry Draper Catalogue of the Spectra of Stars, which is now completed but not yet fully published, contains as many as 225,000 stars. The classification is based on the Harvard system, wherein more than 99 per cent, of all the stars fall into the six main groups designated by the arbitrary letters B, A, F, G, K, and M. It is now known, from the work of Lockyer and Russell, that the actual sequences of changes in a star's spectrum are from M to B as the star increases in temperature (giants), and from B to M as the star cools (dwarfs). Thus for each letter mentioned above there are two distinct kinds of stars, and the nearer the letter is to M the greater this distinction becomes. It is necessary, therefore, to bear this fact in mind when reading the Harvard College Observatory Circular (No. 226) on the relation of spectral type to magnitude by Dr. Harlow Shapley and Miss Annie J. Cannon. Of the numerous tables given in the paper the following abstract of one of them exhibits some of the main results of the investigation.
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Our Astronomical Column. Nature 109, 281 (1922). https://doi.org/10.1038/109281a0
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DOI: https://doi.org/10.1038/109281a0