Cosmic Rays from the Sun 1 



By Thomas Gold 



Professor of Astronomy 

 Harvard University 



[With one plate] 



Cosmic radiation is a phenomenon that has been of the greatest 

 consequence to the development of modern science. Nature provided 

 us there with an incessant stream of very fast and very energetic par- 

 ticles which come into the atmosphere from outer space and which 

 could be put to excellent use. Many of the important discoveries of 

 nuclear physics were made with them, and they have given many times 

 a foretaste of the work that could be done with the great machines 

 the cyclotrons and synchrotrons for which quite properly many 

 millions of dollars are now being spent. 



This stream, as we know now, consists chiefly of protons, the nuclei 

 of hydrogen, which arrive with energies as if they had been subjected 

 to electrical acceleration by a machine giving from 1 billion to 1 bil- 

 lion billion volts. The lower range of energy can just now be matched 

 by the synchrotrons, while the upper energies are very far outside 

 the capabilities of any technical device which we can at present con- 

 template. Although the universe is large and contains many localities 

 that we are still quite ignorant of, it is very difficult to suggest where 

 and how gigantic natural machines of the sort could be at work. This 

 problem is in fact such a great one that one has from time to time 

 wondered whether there is some great gap in our basic understanding 

 of Nature and whether the cosmic rays are perhaps the result of some 

 fundamental process of which we are quite unaware. The alternative 

 is to find within the known fabric of astronomy places and situations 

 where gigantic natural accelerating machines could be at work. The 

 sun has greatly helped us with this. It has demonstrated beyond any 

 doubt that it can make a contribution to this stream of high-energy 

 particles on some occasions. The sun is a steady star, and we are no 



1 Twenty -fourth James Arthur Lecture on the Sun, given under the auspices of 

 the Smithsonian Institution on April 10, 1957. 



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