Temperature Radiation from the Quiet Sun in the Radio Spectrum

Abstract

THE radio-frequency emissivity of the sun considered as black body is proportional to per unit frequency increment, where T is the temperature of the iadiating region, and X is the wave-length of the radiation. The sensitivity of radio equipment is now 6h that it is possible to detect this radiation on th shorter wave-lengths in the radio spectrum. In particular, Reber¹ and Southworth² have measured it on short radio wave-lengths, using highly directive aerial systems. Appleton³ has pointed but that it should be impossible to detect this temperature radiation at the longer radio wave-lengths, owing to the rapid falling off of solar emissivity, combined with the impracticability of using highly directive aerials on these wave-lengths. He and others⁴ suggest that the radiations which are observed on the longer wavelengths, and which appear to be correlated with sun-spots, cannot be thermal in origin, since such an explanation would require solar temperatures of the order one million degrees and upwards. There is little doubt that these views, so far as they refer to temperatures upwards of 106 degrees, must be correct, especially in the light of recent evidence^5,6 showing that at such times the radiation comes from restricted areas in the immediate vicinity of sunspots. It is the purpose of this note to point out, however, that at such wave-lengths we should expect thermal radiation corresponding to values of T downwards from 10 degrees to the familiar surface temperature of order 104 degrees.