Ultra-Violet Solar Radiation

Abstract

The work of Abbot and his colleagues has shown that the radiation from the Sun varies and that the variation is most pronounced in the violet end of the spectrum. Whether we regard the variation as due to a change in temperature, a variable transmission of the outer solar envelope or a variable emissivity, this effect on the ultra-violet is to be expected. Dobson in England using a photographic method, measured the ultra-violet solar radiation transmitted by silver-films on thirty-four days in 1922, and found variations as great as five hundred per cent, and a standard daily range of thirty per cent outside the atmosphere. It occurred to the writer that the uncertainties of photography could be eliminated by measuring the radiation directly with a thermo-couple; that disturbances of the atmosphere could be made differential by standardizing the ultra-violet with the green region of the spectrum which varies only slightly; that the accuracy could be increased by making the apparatus automatic, which would permit an increase in the number of observations, and that the combination of this procedure with the favorable atmospheric conditions on Mount Wilson might lead to results of some interest.