I9I2.] 



AND OTHER CHARACTERISTICS OF STARS. 



571 



means of their " absolute magnitudes " — /. e., the stellar magni- 

 tudes which they would appear to have if each star was brought to 

 the standard distance of 32 light-years (corresponding to a parallax 

 of o".io). The absolute magnitude of the sun on this scale is 

 about 4.7. 



On plotting these absolute magnitudes against the spectral types 

 it becomes immediately evident that most of the stars belong to a 

 series in which the fainter members are redder than the brighter, 

 while a few outstanding stars of each spectral class greatly exceed 

 in brightness those belonging to this series (except for class B, all 

 of whose stars are very bright). The existence of these two series 

 was first pointed out by Hertzsprung/ who has called them by the 

 very convenient names of "giant" and "dwarf" stars — the former 

 being of course the brighter. 



With the large amount of material now available, especially for. 

 the dwarf stars, the results derived from the stars with directly 

 measured parallaxes and from those in the clusters are in striking 

 agreement, as is shown in Table I. 



TABLE I. 

 Mean Absolute Magnitudes of Dwarf Stars. 



Spectrum. 



Stars with Measured Parallaxes. 



Abs. Mag. 



1-7 



Light. 



380. 



42. 



14. 

 2.0 

 2.9 



1-3 



0.55 



0.46 



0.18 



0.04 



O.OI 



Stars in Clusters. 



Light. 



240. 



60. 



50. 



17- 

 5-0 

 3-7 

 1-3 

 0.87 

 0.50 

 0.24 



(0.18) 



Formula. 



Abs. Mag. 



-I.O 

 O.I 

 0-5 



1.6 



2.T 



3.8 



4-5 

 4-9 

 6.0 



7-1 

 8.2 



9-3 



In the above table, the quantity given under the heading " Abso- 

 lute Magnitude " is the mean of the individual values derived from 

 the observed magnitude and parallax of each star in the corre- 



^ Zeitsclirift fiir zcisscnschaftliclic Photographic, Bd. V., p. 86, 1907. 



