The Radio Brightness of the Quiet Sun at 21 cm Wavelength Near Sunspot Maximum

An investigation has been made of the radio emission from the quiet Sun at 21� 2 em wavelength in 1958 (near sunspot maximum). Two different methods have been used, both involving observations with very high angular resolution, to distinguish between the quiet-Sun component and the radiation from localized active regions. In one method, the Sun was scanned with a narrow pencil-beam; in the other, a fan-shaped aerial beam was used to give one-dimensional strip scans. In both cases it was necessary, when analysing the data, to take into account the residual effects of the very intense radiation from the localized sources. The two independent measurements gave results which agree within the limits of error. The apparent disk temperature was found to be approximately 140 000 oK, or twice the value for the same wavelength at sunspot minimum.</jats:p

The Radio Brightness Distribution on the Sun at 21 cm from Combined Eclipse and Pencil?Beam Observations

A study of the brightness distribution on the Sun at 21-cm wavelength on April 8, 1959, is described. High resolution observations were made of the partial eclipse on that day with a simple radiometer of high sensitivity. The brightness distribution of the uneclipsed Sun at the same wavelength was obtained using a cross-grating interferometer, which enabled the bright regions to be located accurately.</jats:p

Solar Radiation at a Wavelength of 3.18 Centimetres

Solar radiation at a wavelength of 3.18 cm. has been measured over a period of three months. The received intensity was found to vary from day to day and the changes are shown to be closely associated with sunspots. The equivalent black-body temperature of the sun over this period, in the absence of sunspots, was 19,300 �K., with a probable error of �7 per cent. The temperature increased by 8 �K. per unit increase of sunspot area (one unit equals 10-5 times the area of the sun's visible disk). This increase is much less than that at longer microwavelengths. Sudden increases of radiation at 3.18 cm., caused by disturbed conditions in the sun, were found to be rare. A number of bursts were observed and a comparison is made with records of longer wave solar radiation and other phenomena of solar origin. Observations were made during the solar eclipse of November 1, 1948 and the results are consistent with either of two simple brightness distributions on the sun's disk. In the first of these, 74 per cent. of the energy is emitted uniformly by the sun's visible disk and the remaining 26 per cent. by a bright ring around the circumference ; in the second, the whole of the radiation comes from a uniform disk of diameter 1.1 times that of the visible sun. </jats:p

Fan-beam Observations of Radio Sources at 21 cm Wavelength

The compound interferometer at Fleurs, N.S.W., has been used in observations of eight of the strongest radio sources, with a fan beam 1'� 53 wide at a wavelength of 21� 1 cm. Each of the sources was scanned from west to east; the brightness distributions in this direction have been observed, and the positions of the sources in right ascension have been determined with high absolute accuracy (probable error less than 1 s of time).</jats:p