SOLAR RADIO ASTRONOMY—MAXWELL 305 
phere. For example, a giant explosion near the solar surface—if at 
the limb of the sun, it is visible as an eruptive, surge, or spray promi- 
nence—will eject intense, fast-traveling shock waves, and jets of fast- 
moving particles. From the slope of the bursts on the film records 
(pl. 2), it is possible to deduce that some of these disturbances travel 
at speeds of approximately 1,000 km. per second. Such disturbances 
frequently continue traveling out from the sun until they reach the 
earth, where they give rise to the magnificent spectacle of the aurora 
APPROXIMATE EMISSION 
HEIGHT (CALCULATED) FREQUENCY 
ee SSS SSS care 
10°kn. ——— mswmm «50 Mc/s (76 ms.) 
OUTWARD 
TRAVELING 
DISTURBANCE 
2010 ke ee ICO Mc/s (2 3m.) 
10S5km = ——~———_ 600 Mc/s (= 0.5m.) 
Figure 2.—Radio model of the solar atmosphere. A disturbance traveling outward 
through the solar atmosphere traverses regions of progressively lower electron density 
and generates radio signals of progressively decreasing frequency. ‘The height figures 
are approximate. 
polaris, and simultaneously disrupt the earth’s radio communications. 
On the average, the Fort Davis equipment has recorded about 30 such 
bursts per year over the sunspot maximum, and about half of them 
have been followed by terrestrial disturbances. 
Other disturbances travel outward at a velocity of about 100,000 
km. per second. These cause very short-lived radio bursts, about 10,000 
of which have been recorded every year of the sunspot maximum at 
Fort Davis. There is at present much speculation concerning the 
nature of the disturbance which gives rise to these radio bursts: 
whether it takes the form of a tremendously fast-moving shock wave, 
or whether it is a stream of particles, 
