Galactic Radiation at 18.3 Mc/s

Abstract

Observations are described of galactic radiation at a frequency of 18.3 Mc/s. over a zone of the sky centred on Declination -34°. The results, expressed as equivalent temperatures, are compared with the distribution of intensity at 100 Mc/s. It is found that the temperatures are consistently much higher at 18.3 Mc/s. than at 100 Mc/s. but the observed ratio of maximum to minimum at 18.3 Mc/s. is less than would have been obtained at 100 Mc/s. using an aerial with the same directional diagram. The observations are consistent with the hypothesis that contours of equal equivalent temperature over the sky are of similar shape on the two frequencies. Peaks in the intensity distribution are observed which appear to be due to discrete sources. The observations give information concerning the attenuation of radiation passing through the ionosphere. It is found that F-region absorption is higher near the critical frequency than expected, and that E-region absorption is lower than expected. It is found that the collision frequency at the height of maximum ionization of the E region is not greater than 10⁴ sec.^-l, and is probably less. For the equipment used, the limit of sensitivity for the reception of radio signals was generally set by galactic noise.