SOLAR RADIATION AND ATMOSPHERE — STETSON 157 



light emitted by hydrogen, there may be photographed on a moving 

 fihn the entire sohir surface so far as it is covered by bright huninous 

 hydrogen clouds. The resulting representations of the sun appear 

 very different from photographs make in ordinary light. Not only 

 are large clouds of hydrogen gas discernible all over the sun, but 

 in the neighborhood of sunspots they often seem to be swept into 

 the heart of the spot as if they were caught in the center of a whirl- 

 pool. Such an appearance might be presented by the top of a ter- 

 restrial cyclone or tornado if photographed from a stratospheric 

 balloon. The dark center of the spot forms the center of the vor- 

 tex; the outlying shaded region that characterizes the so-called 

 penumbra of the sunspot would represent the turbulence bordering 

 upon the central funnel about which the atmospheric particles are 

 rapidly rotating. Thus we see there is a close analogy between the 

 meteorology of tropical cyclones and that of sunspots. To carry 

 the analogy still further, spots north of the sun's equator are in 

 general whirling in one direction while corresponding spots south 

 of the equator whirl in the opposite direction. If the rotation of 

 the one is clockwise, that of the other is counterclockwise. This 

 again is characteristic of the differences of rotation of tropical hurri- 

 canes on the earth originating in the northern and southern hemi- 

 spheres, respectively. 



Had it not been for the trick of splitting up sunlight into isolated 

 frequencies by means of the spectroscope, we should never have had 

 pictures showing the existence of solar vortices such as we have 

 today. In the ordinary photograph of the sun, the light emitted by 

 every chemical element in the sun's atmosphere is clamoring to tell 

 its story. The result is revealed in a rather jumbled picture of 

 what is happening on the sun. The spots show up as dark regions 

 only when the light-emitting power of every element of the sun is 

 damaged in the vicinity of these violently disturbed regions. 



The spectroscope is very much like a highly selective radio re- 

 ceiving set. The sun is a high-powered station sending out light, 

 broadcast in all the wave lengths and frequencies. When we look at 

 the sun or photograph it with a telescope alone, we are using all the 

 light and are, so to speak, operating a radio receiver which admits all 

 frequencies at once. Thus we get a composite but very jumbled picture 

 of what is happening on the sun's surface as far as details are con- 

 cerned. By means of the spectroscope, however, the photographic 

 apparatus, to continue our analogy, must be tuned to a single frequency 

 such as the 470 million megacycle frequency that the red line of 

 hydrogen emits. Tuned to this frequency the spectroscope stills the 

 tumult of all other elements and lets hydrogen tell its own story. It is 

 then that we obtain the clear photographs conveying so beautifully the 

 detailed information about the vortical whirls around the solar storm 



