284 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1957 



There were further surprises in store for the radio astronomer when 

 he looked at the sun at wavelengths of about 1 meter. A steady signal 

 was observed corresponding to a temperature of a million degrees. 

 To find the exact location of the noise source on the sun an attempt 

 was made to observe an eclipse. Providence has so arranged the dis- 

 tances of the earth, moon, and sun that the circular shape of the moon 

 exactly covers the photosphere. Without this fortunate coincidence 

 our knowledge of the sun would for a long while have been quite 



6 MINUTES 



Figure 3. — Radio signals produced by a corpuscular stream as it travels through the 

 atmosphere of the sun. (Photograph taken at the Astrophysical Observatory, Kodai- 

 kanal, India.) 



sparse. As the moon gradually covered the solar disc it was hoped 

 that the radio signal would disappear at a certain stage of the eclipse 

 and thus reveal the radio source. The observations showed little 

 variation in the signal and even at totality the radio sun was still 

 shining. It was obvious that the radio sun was much larger than the 

 optical, and the radiation was coming from the high corona. 



Three types of major radio disturbances are recognized as emanat- 

 ing from the sun. They are noise storms, outbursts, and bursts. A 

 noise storm originates in a cloud in the corona, vertically above a sun- 



