The Starry Heavens 177 



Magnitude of stars. The word " magnitude " does 

 not refer to the actual size of a star, but to its brightness 

 to our eyes. This brightness depends on the distance 

 of the star from us and on how hot it is, as well as on 

 its size. The brightest stars are said to be of the first 

 magnitude ; those barely perceptible, of the sixth magni- 

 tude ; others coming between these classes are referred 

 to as of the second, third, fourth, or fifth magnitude, 

 according to their brightness. One hundred sixth- 

 magnitude stars together would give as much light as 

 one star of average first magnitude. With large tele- 

 scopes stars of the seventeenth magnitude may be 

 seen. Ten thousand such stars together would not give 

 light enough to be visible to the unaided eye. 



The number of stars of the smaller magnitudes is 

 much greater than the number of stars of large magni- 

 tude. Those of the first six magnitudes to be seen 

 north of the celestial equator, or within 35 degrees to 

 the south of it, have been divided as follows : 



First magnitude, 15; second magnitude, 48; third 

 magnitude, 152; fourth magnitude, 313; fifth magni- 

 tude, 854 ; sixth magnitude, 2010. 



The first-magnitude stars differ in brightness, Sirius, 

 the Dog Star, being more than 10 times as bright as 

 Aldebaran, which is of standard first magnitude. In the 

 following list the fifteen first-magnitude stars visible 

 in the Middle states and farther north are arranged 

 in the order of their brightness. Those preceding 

 Aldebaran are brighter than standard first magnitude ; 

 those following Aldebaran are less bright than the 

 standard of their class : 



