STORMY WEATHER ON THE SUN — W. 0. ROBERTS 173 



The coronagraph of the High Altitude Observatory has been op- 

 erated at Climax ever since it was first established there in 1940 by 

 Donald H. Menzel. This instrument has played a modest but import- 

 ant role in our study of the sun. For example, work conducted jointly 

 by Alan Shapley, then of the Department of Terrestrial Magnetism of 

 the Carnegie Institution of Washington, and myself in the years of the 

 last war, led us to uncover a new relationship between the bright re- 

 gions of the sun's coronal emission as determined from spectra of the 

 sun's limb (sec pi. 1, fig. 2) and the behavior of magnetic storms, with 

 their associated aurorae, erratic compass-aiming, and the related dis- 

 turbances of radio communications. We found that during the years 

 of minimum sunspot activity, whenever a region of very bright coronal 

 emission passed the east edge of the sun, moved along by the 27-day ro- 

 tation of the sun, it tended to produce magnetic storms 2 or 3 days later. 

 These storms thus occurred when the coronal emission presumably re- 

 sponsible for the disturbance was still located in the east half of the 

 sun's face. So far, we are at a loss to explain why the corona should 

 be in this preferred location on the sun at the time of producing its 

 maximum effects. 



Another discovery made with the Climax coronagraph was that of 

 the tiny chromospheric spicules. These spicules are tiny jetlike prom- 

 inences of very short lifetime and very simple structure. I first noted 

 these tiny prominences in 1942, and found them to be most pronounced 

 in the regions of the poles of the sun, where the normal prominence 

 activity is very minor. The spicules seemed to be consistently directed 

 outward, along radii from the center of the sun. A typical spicule, 

 like that shown in plate 2, forms as a little bubble which then bursts 

 and jets outward to a height of perhaps 10,000 miles. The entire life- 

 time of a spicule lasts only something like 4 minutes on the average. 

 The spicules seem the only major evidence of prominence activity that 

 transports mechanical energy consistently in the outward direction 

 through the solar surface to the atmosphere of the sun. We think 

 that perhaps their role in the heating of the sun's corona may be sig- 

 nificant. Also from the Climax coronagraph have come many thou- 

 sands of feet of motion-picture films of prominences. These films, 

 similar to the excellent pictures taken with the spectroheliograph at 

 the McIMath-Hulbert Observatory, and taken by means of the motion- 

 picture technique developed by McMath, show very graphically the 

 violence of the behavior of the gigantic solar "storms" that charac- 

 terize solar "weather." These motion-picture films, as I have already 

 stated, form the main body of observational material used by Menzel 

 in deriving his new theories for the activity of the stormy atmosphere 

 of the sun. 



