260 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1961 



flare, the entire X-ray spectrum was observed to brighten to many 

 times its normal intensity. At the shortest wavelengths, the increases 

 were orders of magnitude greater, although the energy content was 

 only a small portion of the total X-ray output. X-ray quanta with 

 energies up to 125,000 electron volts appeared, whereas the normal 

 short-wavelength limit was of the order of a few thousand electron 

 volts. From the spectral distribution of the observed X-ray emission, 

 it is possible to speculate about the mechanism involved in its produc- 

 tion. If it is assumed that the enhanced X-ray emission resulted from 

 a heating of the coronal gas, a temperature as high as 10^ degrees K. 

 would be required. Alternatively, the spectrum could have been pro- 

 duced by streams of suprathermal electrons injected into cooler gas at 

 a temperature not exceeding 10^ degrees K. To choose between such 

 widely divergent models will require much more detailed spectral 

 information than has been obtained thus far. The energy radiated 

 as X-rays represents a major portion of the total energy output of a 

 solar flare and is entirely adequate to explain the accompanying ion- 

 ospheric disturbances, such as the shortwave fadeout and sudden 

 phase anomaly. 



During the year 1960, a major step forward in the study of X-ray 

 emission from solar flares was accomplished by the launching of the 

 first satellite observatory by the U.S. Naval Research Laboratory. 

 The satellite, called Solar Radiation I (1960 Eta 2), carried two 

 ionization chambers to measure solar Lyman-a (1216 A.) and X-rays 

 (2-8 A.) . These detectors were momited on the equator of the spher- 

 ical satellite, to which was imparted a high spin rate upon separation 

 from the launching vehicle. Each detector viewed the sun once per 

 revolution, giving a spin-modulated signal which was transmitted 

 continuously. 



Figure 4 illustrates a sample record obtained during the passage of 

 the satellite over Blossom Point, Md., on August 6, 1960, almost simul- 

 taneously with the start of a Class 1 flare, which lasted 18 minutes. 

 Lyman-a signals are indicated by upward deflections from the mid- 

 scale zero level. X-ray signals deflect downward. On the pass illus- 

 trated by the first strip of telemetered signals, the sun was quiet. A 

 steady Lyman-a signal is indicated, but only the barest trace of X-ray 

 intensity. As the satellite returned one orbit later, telemetry recep- 

 tion began almost in coincidence with the eruption of the flare at 

 1506 UT. At 1509 UT, the X-ray emission began to increase. Ion- 

 ospheric observations and cosmic-noise measurements showed simul- 

 taneous starts of various ionospheric disturbances. Between 1510 and 

 1511 UT, while a microwave outburst occurred, the X-ray flux in- 

 creased rapidly to full scale and remained at that level until flare 

 maximum in H-a was reached at 1514 UT. Shortly afterward, the 



