4 6 



STELLAR PROBLEMS. 



These examples will suffice to illustrate the 

 character of the solar work in progress on Mount 

 Wilson. Let us now consider for a moment the 

 broader bearing of these results, each of which has 

 a wide range of application. Thousands of stars, 

 in the same stage of evolution as the sun, doubt- 

 less exhibit similar phenomena, w r hich are hidden 

 from us by distance. No possible increase in the 

 power of our telescopes, so tar as can be judged 

 from present knowledge, will ever render star 

 images comparable in size with the solar image. 

 But the knowledge derived from the study of the 

 sun prepares us to solve problems otherwise much 

 more difficult. For example, the results of the 

 work on sun-spot spectra, in harmony with other 

 phenomena, render it safe to attribute to reduced 

 temperature the bands and the weakened and 

 strengthened lines in the spectra of Arcturus and 

 other stars. This conclusion will assist in arrang- 

 ing the stars on a temperature basis, showing the 

 gradual changes they have passed through in the 

 different periods of their existence. Again, the 

 peculiar behavior of certain lines in the sun has 

 recently led to the detection of an interesting 

 relationship between a star's spectrum and its 

 absolute magnitude, which provides a new and 

 very effective way of determining stellar distances 

 and throws much new r light on the evolution 

 problem. 



