A distribution of solar radio brightness at a wavelength of 21 cm has been derived from observations made during the period of low sunspot activity from 1952 to 1954. The observations were made using two multiple interferometers arranged at right angles; this enabled the solar disk to be scanned in many different directions. The derived one-dimensional profiles of the quiet Sun for these various scanning directions were combined and a Fourier method adopted to derive a two-dimensional brightness distribution. The distribution shows marked limb-brightening in the equatorial zones but none in the polar regions. The contours of brightness are in general conformity with those expected from a solar atmosphere having a coronal electron density distribution of the kind proposed by van de Hulst for the period of minimum sunspot activity.
SummaryA large number of highly emitting regions on the Sun have been studied individually by means of a 32-element interferometer which produces fringes 3 min of arc wide at a wavelength of 21 cm. These regions are responsible for the slowly varying component of the solar radiation at decimetre wavelengths.The radio sources appear always to be associated with plages faculaires and, during the years 1952-53, were found to lie about 22,000 kIn above them. The observations showed that the sources, when resolved, appeared to have the same size as the associated plages.The angular distribution ·of flux from radio sources was found tb follow approximately a cosine law, which suggests that a source has the form of a thin sheet, lying parallel to the surface of the Sun.The observations throw light on conclusions reached from the statistics of whole-Sun observations. A high correlation exists between radio flux and sunspot area in an active region in the period when both are near their peak. In the period of decay, however, the radio flux decreases more slowly than the sunspot area.
SummaryA new aerial system of very high resolving power has been designed for use in determining the distribution of radio brightness across the solar disk at a wavelength of 21 cm. Thirty-two aerials with paraboloidal reflectors are evenly spaced in an east-west direction over a distance of about 700 ft., and are connected by a branching system of balanced open-wire transmission lines to a receiver. The aerial system produces multiple beams each 3' of arc wide and spaced 1.7° apart. The rotation of the Earth causes one after another of the aerial beams to scan the disk of the Sun.The record obtained from the radio receiver gives a one-dimensional brightness distribution over the solar disk.
SummaryDaily records of one· dimensional distribution of radio brightness over the Sun are obtained in the way described in Part I of this series (Christiansen and Warburton 1953). When superimposed, these records show a well·marked lower envelope which remains substantially the same, in shape and size, over a period of months. This envelope gives the brightness distribution over the "quiet" Sun. The direction of scan, with respect to the position of. the solar axis, changes during a year by more than 50°. The very small change in shape of the envelope during this period suggests that for purposes of preliminary calculation the brightness distribution may be assumed to be circularly symmetricaL The radial distribution of brightness, calculated on this basis, is found to show marked limb· brightening and to be consistent with the calculated brightness distribution for a simple solar model in which the assumed values of temper. ature and density are .close to those commonly accepted.
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