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.
A preliminary survey of 1420 Mc/s. hydrogen-line emission has been
made over 270� of galactic longitude extending through the galactic centre, and
anticentre. The radiation source is in the form of a band of varying intensity
along the galactic equator. The maximum brightness temperature is about 100 �K,
in the direction of the galactic anticentre.
Measurements of
line-profile show considerable variation, with a minimum width of 0.12 Mc/s.
Double lines are evident between galactic longitudes 170 and 240� and it is
suggested that these may originate in major structural features of the Galaxy.
The change in the peak
brightness of the line along the galactic equator may result from line
broadening due to galactic rotation. On the other hand it may reveal the existence
of highly emitting regions. The latter interpretation is supported by the
agreement in position of the bright areas for both the line emission and the
continuous spectrum galactic emission.
Radio-frequency power received from the
sun at a wavelength of 50 cm. was measured at three well-separated places
during the solar eclipse of November 1, 1948. Abrupt changes in slope on the
records of received flux density were interpreted as being the result of the
covering and uncovering on the sun of small areas of great radio brightness.
These areas were found to be associated with some visible sunspots, with
positions previously occupied by sunspots, and with one prominence. The average
effective temperature of the bright areas was about 5 X 106 �K., and
the are= contributed a total power of roughly one-fifth of that from the entire
sun.
After the effects of active areas had been
taken into account, the remaining four- fifths of the power received from the
sun was found to originate from a source larger than the visible disk. About 40
per cent. of the power from this source originated outside the edge of the
visible disk. The results were consistent with a theoretical distribution of
brightness on the source, which involved limb-brightening.
The relative magnitudes of the two
circularly-polarized components of the solar radiation showed small differences
as the bright areas were eclipsed. No predominance of one component was seen
when one hemisphere of the sun was eclipsed ; hence no effects of any general
magnetic field on the sun were detected.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.