MIRACLES OF SCIENCE 



another familiar example is the bright star Arcturus. 



At a still later stage the star becoming yet cooler 

 takes on a reddish glow, and its spectrum shows char- 

 acteristic bands of carbon. Betelgeuse and Mira are 

 familiar examples. 



The stages of this evolution require unthinkable 

 billions of years, but there seems to be no escape from 

 the conclusion that each and every star is destined 

 ultimately to be blotted out in darkness, reaching a 

 condition, in other words, of which we have examples 4 

 on a small scale in the present state of the moon and 

 of the earth itself. 



So far as present knowledge goes there is only one 

 way in which a star that has thus become cold and 

 dark can be rejuvenated, and that is by collision. 

 There would seem to be no reason, however, why any 

 given star might not undergo the process of collision, 

 nebula formation, slow cooling, and extinction, over 

 and over. During each time of brilliancy it would 

 lose some of its substance an'd its energy through 

 radiation; but on the other hand, new matter must 

 come to it constantly in the form of cosmical clust; 

 and renewed energy may be accumulated through 

 momentum acquired in falling through space say 

 toward the gravitation center of the universe. 



So the cyclic process might conceivably go on for- 

 ever; or at all events until some unthinkably remote 

 epoch of the future when all the gravitational matter 

 in the universe has been aggregated into a single 

 mass. Meantime it would seem as if the periods of 

 darkness for each individual star must be indefinitely 

 long in comparison with the periods of brightness. 



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