It is usual to describe the motion of the planets around the sun in terms only of the gravitational forces between them. The purpose of this note is to point out that another form of interaction between bodies in the solar system is possible through the medium of the solar wind.

In this preliminary study the first two-dimensional pictures showing detailed features of the quiet Sun and weak but moderately stable structure at metre wavelengths are presented. The observations were made at 80 MHz with the Culgoora radioheliograph.

Absorption limits the distances at which X-ray sources may be observed at low photon energies (≲3 keV). Several authors have estimated the X-ray absorption coefficients of the interstellar medium by assuming a chemical composition such as that given by Aller for the general abundances of the elements.

A knowledge of the quantitative chemical composition of the primordial solar system must underlie all comprehensive studies of its origin and evolution. Usually we take the composition of the surface layers (photosphere) of the Sun as representative of this composition (except perhaps for deuterium, Li, B, and Be).

The innermost Galilean satellite of Jupiter, Io, has been observed to strongly modulate the probability and intensity of Jupiter’s decametric emissions. The effect is most pronounced at frequencies greater than 30 MHz. Radiation occurs from two configurations of Jupiter and Io, the first when Io is 90° from superior geocentric conjunction (s.g.c.) and Jupiter’s longitude is near 120°, and the second when Io is 240° from s.g.c. and Jupiter’s longitude is near 230°.

Solar X-ray bursts observed by a proportional counter carried on the IMP-F satellite have been analysed for correlation with optical Hα flares and radio bursts. The solar X-ray flux at energies greater than 3 keV was measured each 82 seconds and consisted of impulsive bursts superimposed on a slowly varying X-ray background. During June and July 1967 there were an average of ~10 bursts per day with intensities greater than 400 photons cm−2 s−1 (2 × 10−6 erg cm−2 s−1) which was the threshold for observation of a burst.

Observations were made on 1970 February 9 using the Culgoora magnetograph to study the configuration and evolution of magnetic fields in a solar active region with high time resolution. The region observed was located at N20 E25 at the beginning of the observations which commenced at February 8, 22h 59m U.T. and finished at February 9, 07h 24 m. The magnetic fields were observed in the light of Cal 6102.7Å. Over a wavelength range corresponding to an intensity from 1/8 to 1/2 of the way up from line centre to the continuum on the blue side of the Une there is no apparent change in the field configuration, and the observations were made at a wavelength corresponding to the mid-point of this range. Exposures were made approximately every two minutes, with occasional large time gaps for instrumental adjustments.

A class 2 flare began on 1968 June 9 in the active region near 17°N 40°E, at about 00h15m U.T., maximum 00h37m, terminating about 02h30m. The event was recorded at Culgoora with the 5-inch flare-patrol and 12-inch chromo-spheric telescopes at solar diameters and frame intervals of 16 mm/10 s and 17 cm/3 s respectively. Both telescopes used Halle filters, pass bands about 0.5Å centred on Hα, and Duplopan 35 mm film. The seeing was mediocre, with occasional fairly good frames.

Observations of transient solar radio emissions lasting 0.2 to 2 s in the frequency range 25-50 MHz have demonstrated the existence of a characteristic and relatively common type of burst (the split pair) made up of two narrow band components separated in frequency by about 0.1 MHz.

The small group of known Seyfert galaxies (Seyfert 1943) is of interest because it is clear that some violent activity is occurring in the nucleus, and some of the properties suggest a relationship with quasi-stellar sources. The spectrum of a Seyfert galaxy consists of strong, often very broad, emission lines superposed on a continuous spectrum which in some cases shows no absorption-line features. Two of the galaxies, NGC 1068 and 1275, are radio galaxies and the latter is known to be variable at radio frequencies (Dent 1966).

In this paper 80 MHz heliograph observations are described of a remarkable solar outburst on 1969 March 30 initiated by a flare on the invisible hemisphere of the Sun. The event raises several questions of theoretical interest, in particular the implication that the magnetohydrodynamic waves responsible for certain type II bursts must travel along curved paths.

Transit observations of the Sun can be made with the Molonglo radio telescope which is now in full operation at 408 MHz. Thus the Sun can be scanned once per day by eleven separate beams evenly spaced in declination. Because of foreshortening of the north-south arm with increasing zenith angle, the total coverage varies and in winter about 28′ arc can be covered by the eleven beams, whereas only 15′ is covered in mid-summer. This also means that the beamwidth in declination changes from 2′.9 at the zenith to about 5′.8 for the mid-winter sun. The beam is 2′.8 wide in right ascension. A further complication is the fact that the positions of the eleven beams cannot be chosen arbitrarily but can only be selected from a predetermined set of beam positions. These latter have been fixed by the phasing connections built into the telescope and cannot be changed easily. Hence for all the above reasons the strip of Sun which can be scanned will vary from day to day.

In 1961 Fokker and Roosen suggested that the concept of homology as applied to solar optical flares by Ellison, McKenna and Reid could be extended to flare-associated radio events as well, since successive flares within the same centre of activity sometimes produce radio bursts which look remarkably similar on single-frequency records. Teresa Fortini reported very similar ionospheric responses due to X-radiation from flares recurring in the same active region. In 1950 Wild noted similarities in the dynamic spectra of type III bursts occurring within periods of minutes.

The outburst and storm of more than four hours’ duration that accompanied the importance 2 flare beginning at 0h25m U.T. on 9 June 1968 were observed at 80 MHz with the Culgoora radioheliograph. More than 104 heliograms in both senses of circular polarization were recorded at one-second intervals both as cathode-ray-tube photographs and as digital characters on magnetic tape. It is the purpose of this preliminary account to summarize these observations and bring attention to a new phenomenon observed before the start of the flare.

Type II solar bursts characteristically drift slowly from high to low frequencies at a rate of about 0.1 MHz/s, appear only at frequencies lower than 250 MHz, and frequently have harmonic structure, i.e. there are identifiable spectral features within the fundamental which are duplicated at twice the frequency. Thus it is clear that at least in some cases, true harmonic radiation is involved; the source region emits frequencies f and 2f simultaneously.

This year the School of Electrical Engineering began observations with the new Fleurs compound interferometer. This instrument operates at 21 cm and has a fan-beam response 35″ arc wide in an east-west direction.

The Stellar Interferometer at Narrabri Observatory consists of two large reflectors which focus the light from a star on to two photoelectric detectors. The output currents from these detectors contain fluctuations which correspond to fluctuations in the starlight itself. The fluctuations from the two detectors are amplified in the frequency range 10-100 Mc/s and their correlation is measured by a linear multiplier. This correlation is measured as a function of the separation between the two detectors. It can be shown theoretically that the correlation at any given baseline is proportional to the square of the fringe visibility which would be observed by a classical Michelson interferometer. It is therefore possible from observations of the correlation at different baselines to find the angular diameter of a star.

This programme was undertaken because the preliminary observations of Beta Centauri with the Narrabri stellar interferometer (Hanbury Brown, Davis, Allen, and Rome) show that the correlation received is not consistent with that expected from a single star. The Lick Catalogue of Radial Velocities states that β Cen is a Bl II star. The Narrabri results are consistent with several models; in particular, it may be a double star with components of similar brightness, or it may have a very luminous, extended atmosphere or shell surrounding it. The latter possibility is perhaps unlikely on the spectroscopic evidence, as there are neither emission nor sharp absorption components in the spectral lines.

Since the advent of the 80 MHz radioheliograph, precise position and polarization measurements have become available on several moving type IV bursts. Two of the more puzzling characteristics of these bursts are : (1) they exhibit strong circular polarization in parts or all of the source region ; (2) after moving outward to as much as 3 R⊙ with relatively constant intensity, they rapidly fade away. In this paper we discuss the polarization and intensity of synchrotron radiation from mildly relativistic electrons and suggest betatron deceleration as a mechanism to explain the rapid fade-out of the moving type IV sources. The results are applied to two examples of moving type IV bursts.

This paper is a preliminary account of the calculation of the circularly polarized synchrotron radiation received from a distribution of electricallycharged particles confined to a thin shell in the magnetic field of a dipole. Calculations of the total radiation and the degree of linear polarization have previously been carried out, and these calculations are duplicated in part.