I9I2.] 



AND OTHER CHARACTERISTICS OF STARS. 



573 



formula for the corresponding spectral class, while 150, or 69 per 

 cent., have absolute magnitudes within one magnitude of the com- 

 puted value. 



The series of stars so far discussed does not however comprise 

 all those in the heavens. Most of the stars of the first magnitude 

 have small parallaxes, and are of great absolute brightness ; and 

 a study of proper-motions shows the same to be true of the naked- 

 eye stars in general. It follows that there exists another series of 

 stars, of great brightness, differing relatively little from one spectral 

 class to another. These " giant " stars can be seen at enormous dis- 

 tances, and consequently form a wholly disproportionate part of the 

 stars visible to the naked eye, as has been explained above. The 

 illustration there given greatly understates the actual situation for 

 the redder stars. The dwarf stars of class M, for example, are so 

 faint that not one of them is visible to the naked eye (though one 

 of them is the second nearest star in the heavens), and so the 

 naked-eye stars of this class are all " giants." 



Relatively few of these giant stars are near enough for reliable 

 measures of parallax, and even for these it is safer to take the mean 

 observed parallaxes and magnitudes of groups of stars, to diminish 

 the effect of errors of observation. Confining ourselves as before 

 to parallaxes determined by two or more observers, or by observers 

 of high accuracy, the existing data may be summarized as follows. 



TABLE II. 

 Mean Absolute Magnitudes op Giant Stars. 



The stars of class B are repeated here, since they may be re- 

 garded as belonging to either series. 



