STELLAK LABORATORIES 



By Theodobe Dunham, Jr. 



[With 1 plate] 



A thousand years ago the stars were looked upon as fixed points 

 of light permanently attached to the sky. A few brave minds dared 

 to imagine them as more than this, but without accurate measuring 

 instruments there could be only speculation as to the true nature of 

 points of light. At present we look upon the stars as huge aggrega- 

 tions of matter, extremely hot and probably gaseous to the very 

 center, held together by the mutual attraction of their separate par- 

 ticles and radiating away great quantities of light and heat. Where 

 the ancients saw a single star, the increasing power of our telescopes 

 has shown us more and more stars, until now we know many millions 

 for each of theirs. One may perhaps ask why we arc interested in 

 knowing more exactly how the stars are built and what goes on below 

 their surfaces. 



In the first place there is our natural curiosity. The stars appear 

 to be the parents of the planets, and so of all life in the universe. We 

 ourselves are, in the last analysis, made up of minute particles which 

 were once probablj^ parts of a star — the sun. Millions of j^ears ago 

 the outer layers of the sun were as now, a swarm of atoms, so hot that 

 no two could hold together long enough to build anything more or- 

 ganized than local eddy currents. We believe that suddenly another 

 star, another great hot globe of gas, then swept hj. It passed close 

 enough to raise great tides in the sun and even to tear loose parts of 

 the sun's outer layers. The passing star kept on, but the clouds of 

 atoms, torn loose from tlie sun, had to face new conditions. 



As they circulated in paths at various distances from the sun, 

 they necessarily began to cool. As they cooled, their atoms began 

 to hold together in groups of different kinds, and what had once 

 been clouds of disorganized atoms torn from the sun slowly became 



1 Lecture delivered on Feb. 10, 1031, in Culbertsou Hall, California Institute of Tech- 

 nology, Pasadena, under the auspices of the Astronomical Society of the I'aciOc and the 

 Mount Wilson Observatory, Reprinted by permission from Publications of the Astro- 

 nomical Society of tlie Pacific, vol. 43, No, 252, April, 1931. 



102992—32 18 259 



