SUN SPOTS AND RADIO RECEPTION^ 



By Haklan T. Stetson 

 Director, Perkins Obnerrutury, Ohio Weslcyan University 



[With 2 plates] 



Of all astronomical bodies the sim is by far of the greatest imme- 

 diate concern to human beings. Literally in him we live and move 

 and have our being. Every square yard of the earth's surface 

 exposed to direct sunshine receives energy at the rate of more than 

 one-and-a-half horsepower; the whole earth receives from the sun 

 heat at such a rate that if converted into doing work it would 

 represent the equivalent of 230,000,000,000,000 horsepower. With 

 the exception of a few experimental solar engines once set to work 

 for irrigation purposes in arid regions, man has practically made 

 no attempt to convert, directly, solar rays into mechanical effort. 

 Perhaps when oil is running low and coal is $100 a ton we may 

 learn to tap profitably this abundant source. 



When we reflect, further, that, after all, the whole earth can 

 intercept less than one-billionth of the sun's total output, we realize 

 our complete inability to conceive of this stupendous and seemingly 

 inexhaustible supply. To determine conditions at the surface of 

 the sun and to measure its temperature, which is about 12,000° F., 

 is a far simpler task than to divine the source of its enormous 

 energy or to conjecture just what is going on in the interior. 



However, the sun is a typical star, and, thanks to the researches 

 of Eddington at Cambridge University, we are no longer as igno- 

 rant as we once were concerning the interior of the stars, and our 

 best guess as to the source of their radiant energy leads us into the 

 very structure of the matter of which stars are made. We may pic- 

 ture the interior of the sun as a veritable hurly-burly of atoms and 

 electrons, flying hither and thither at terrific velocities which rapidly 

 increase as the sun's center is approached, where the temperature is 

 of the order of 80,000,000°. From this hot interior of the sun 

 must ultimately arise the source of solar radiation, which not only 



1 Revision of paper originally presented at a meeting of the Franklin Institute held 

 Thursday, Feb. 13, 1930. Reprinted by permission, with change of title and other revi- 

 sion, from the Journal of the Franklin Institute, October, 1930. 



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