184 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1952 



tion cannot be accounted for by radiation from discrete radio stars, 

 then it is necessary to postulate radiation from the interstellar matter. 

 Although the possibility of this has been considered in some detail, 

 it cannot be said that any theory which would explain the observed 

 intensity has yet been advanced. 



When we seek a mechanism to explain the radiation from the ob- 

 served discrete radio stars, we first notice that they differ from the 

 sun in that they radiate comparatively much more strongly in the 

 radio frequencies than in the visible part of the spectrum, as if they had 

 photospheres which are much cooler than the sun and coronas which 

 are much hotter. But no detailed theory has yet been accepted to 

 explain them. 



It appears likely that, in the immediate future, experimental radio 

 astronomers will concentrate their attention on devices for achieving 

 increased angular accuracy, in an attempt to observe more radio stars 

 and, if possible, to measure their parallaxes and angular sizes. A 

 search for the emission of characteristic "line" spectra from the galaxy 

 and from the sun will also probably be carried out, particularly in 

 view of the most interesting recent discovery that waves of length 21 

 cm. can be observed, owing to hydrogen, in certain directions in the 

 galaxy. On the theoretical side, attention will probably be directed 

 toward theories to explain the radiation from sunspots and from radio 

 stars. 



Reprints of the various articles in this Report may be obtained, as long as 

 the supply lasts, on request addressed to the Division of Publications, Smith- 

 sonian Institution, Washington 25, D. C. 



