We consider the linear and non-linear evolution of a perturbed X-type neutral point. A semi-analytic treatment is given for the case of small disturbances of the equilibrium field. This problem admits well defined azimuthal modes which allow a formally exact determination of the magnetic annihilation rate. It is shown that the longest lived modes are purely radial and decay of the timescale τ ≈ |ln η| where η defines the resistivity of the coronal plasma. Higher azimuthal modes decay much faster, generally on a fraction (O(m −1)) of the Alfvén timescale for the outer field.

We go on to perform finite amplitude calculations that demonstrate the implosive current build-up that precedes the reconnective phase of the relaxation. In general both linear and non-linear studies support the idea of an initial implosive stage which rapidly releases the bulk of the energy associated with arbitrary field disturbances.

The radioheliograph at Culgoora has recently been used to investigate the interesting changes which take place in the amplitudes of the pulses from PSR 0950+08, 1133+16 and 1919+21. The experiments had two main objectives: (i) to investigate the temporal changes in the spectrum near 80 MHz; (ii) to search for periodicities in the pulse amplitudes with periods extending up to one or two minutes.

The cyclotron line in Her X-1 is a hard X-ray feature at ≈ 58 keV discovered by Trümper et al. (1977). A cyclotron emission line at about this energy had been predicted by Gnedin and Sunyaev (1974) and Basko and Sunyaev (1975). They developed a model for the infall of accreted matter onto a magnetized neutron star’s surface, and concluded that hot spots would form at the polar caps and radiate X-rays. They predicted that the optional depth for bremsstrahlung would be less than unity, that for Compton scattering greater than unity and that for cyclotron absorption much greater than unity. A cyclotron line is then implied due to the emission spectrum lying below the black-body spectrum except near the cyclotron energy where it rises up to the black-body limit. More recent developments of these background ideas have been reviewed by Börner (1980).

On 1968 October 30 a large solar flare (importance 3B to 4B) began at approximately 23h42m U.T. We present here a preliminary account of the associated radio emission.

It has been recently suggested (Crawford 1979) that there is an interaction between a photon and curved space-time that can be observed as a redshift of the photon frequency. Since the amount of the redshift is a function of the curvature it may be used to discriminate between gravitational theories. This is easily done using the parametrized post-Newtonian (PPN) limit fully described in the review article by Will (1972).

This paper presents a brief discussion of the AAT data on SN 1987A and its archive.

The ionosphere does not behave like a smooth mirror for radio waves, but more like an irregular diffracting screen. When a radio wave is reflected from it, a random diffraction pattern is formed over the ground. Simple arguments can be used to show that this pattern will move over the ground with a velocity which is twice the horizontal velocity of the ionosphere. This phenomenon can be used for the detection of movements taking place in the ionosphere.

Barred spirals are well-known to include several ‘distinct components’ or morphological structures in the light distribution (Sandage 1961; de Vaucouleurs 1959; Kormendy 1979). In addition to the bar, spheroid, and disk components, one often observes ring-like enhancements at discrete relative positions within the disk. These inner rings (r), outer rings (R), and nuclear rings (nr) have been the subject of recent, fairly intensive observational (Buta 1984a; Kormendy J979; de Vaucouleurs and Buta 1980a,b; Athanassoula et al. 1982) and theoretical (Schwarz 1979,1981,1984a,b,c; Simkin, Su, and Schwarz 1980) research, and it now seems well-established that most rings are linked to dynamical resonances with the bar.

Reverse drift pairs were first described by Roberts (1958) and later by Ellis (1969) and de la Nòe and Moller-Pedersen (1971). Figure 1 shows a 10-min section of the spectrograph record and the corresponding section of the polarimeter record. The figure contains several reverse drift pairs and illustrates the main features of RDPs, namely: (1) frequency drift rate of about 4 MHz s-1 (i.e. a factor of ~50 faster than Type lis and a factor of ~2 slower than type Ills); (2) drift to higher frequencies (i.e. opposite to that of Type II and III bursts, hence the name ‘reverse’); and (3) an apparent ‘echo’ of the burst some 1 to 2 s later to form a pair. On 1979 February 17/18 a noise storm consisting of Type 1 bursts, Type III bursts and an underlying continuum was observed with the Culgoora spectropolarimeter, spectrograph, and radioheliograph. During this noise storm, the spectrograph record showed several hundred RDP bursts, and about fifty FDPs. Here we report new results on the polarization-of drift pair bursts, present further data on RDP positional and frequency characteristics, and then comment on existing theories concerning RDPs.

The physical properties and spatial distribution of 12 pulsars discovered with the Molonglo radio telescope have been discussed by Mills. Several more pulsars have been detected and details will be published when the measurements are complete. Parameters of a recently discovered pulsar, MP 0628, are given in Table I. All the Molonglo pulsars have been found by visual examination of chart records. The use of pulse lengthening circuits to improve the visibility of pulsars on slow charts, and the continuation of the observations over several hundred hours with the greatest available sensitivity have been factors contributing significantly to the success of the Molonglo pulsar search.

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.

Type I storms are the most frequently observed solar phenomena at metre and decimetre wavelengths. Since the first identification of the emission of this type with a large sunspot group a great many type I storms have been recorded with radio-spectrographs, polarimeters and interferometers (see, for example, Wild, Smerd and Weiss, Kundu, Wild). Nevertheless, we can offer no satisfactory answers to the most fundamental questions about type I storms: ‘What kind of disturbances supply energy to a localized coronal region to maintain the storm activity for up to several days?’; ‘What is the emission mechanism responsible for the peculiar features observed in type I storms?’.

Detailed physical mechanisms responsible for excitation of spectral lines in gaseous nebulae have been known for 50 years, and reasonable estimates of nebular densities and temperatures were obtained in the late thirties and early forties. However quantitative chemical analyses have proven difficult partly because of uncertainties in atomic parameters (notably collision strengths) and partly because of complications posed by the nebulae themselves.

A spectrum analyser based on SAW (surface acoustic wave) devices has been developed for Jupiter, solar and pulsar observations. It has an overall frequency range of 100 MHz and a frequency resolution of 30 kHz. A complete spectrum is produced every 80 μs. It is initially being used with a 4000 dipole broadband array in the frequency range 30-130 MHz and for Jupiter observations from 8-38 MHz.

For many years we have had evidence from solar radio bursts of violent mass motions in the solar corona: type II bursts reveal the passage of shock waves through the solar corona, and moving type IV bursts show that plasma and magnetic field travel to great distances without any sign of slowing down.

Temporal and spatial characteristics of solar flares are briefly reviewed in this paper. The global, temporal and spatial behaviours of flares are given first. Besides the 154-day periodicity, an 80-day periodicity of occurrence rate of large hard X-ray bursts for the period 1980 February – 1985 December, and the delay of the peak occurrence rate of large flares are pointed out, then the gregariousness of major flares is shown. In the third section, the time process and spatial structure of individual flares are shown and described according to space and ground-based observations. In the last section two problems on flare properties are discussed. (i) Previous classifications of solar flares are based generally on observations in a single spectral region. A new classification of flares based on observations in multi-spectral regions is given. (ii) Energy released in part of a loop seems to be not enough for a whole flare, and a qualitative model in which the energy is supplied by the untwisting of magnetic fields is proposed.

In 1931 Karl Jansky established that radio noise was associated with our own galaxy–the Milky Way. For a decade and a half there was little follow-up; those of us who were associated with low frequency radar during the war regarded it as a nuisance which could limit the detection range of enemy aircraft. Grote Reber was the first to make a detailed but fairly low resolution map of the radiation from the galaxy showing, for the first time, some detailed structure. The event which we celebrate today occurred when Gordon Stanley, Bruce Slee and I showed that three of the discrete sources that we had discovered could be identified with visual objects. One was with the Crab Nebula, a supernova remnant within our own galaxy and the other two with galaxies, far beyond our own system, in the constellations of Virgo and Centaurus. Thus began extragalactic radio astronomy. In 1982 at the Noosa meeting of the ASA, I gave an account of those early years, later to be published in the ASA Proceedings. As I don’t wish to repeat myself, I propose to speak on my involvement in a later development which was to extend the observable scale of the universe to look-back times as great as the age of the oldest stars in our own system. The first important step was Graham Smith’s identification of Cygnus A with a galaxy that was much fainter than our two. The spectrum by Minkowski revealed an instrinsically highly-luminous galaxy with strong emission lines and opened up the possibility of discovering similar objects at significantly greater distance. This was achieved nine years later with the building of the Owens Valley Observatory and my title of ‘Radiophysics in Exile’ comes from the fact the observatory owed its existence and early successes very largely to past and future staff members of Radiophysics. They were, in order of appearance, J. G. Bolton, G. J. Stanley, K. C. Westfold, J. A. Roberts, V. Radhakrishnan, D. Morris and K. I. Kellermann. Some still bear . the scars–Westfold left the tip of one index finger in the Owens Valley!

The original concept of the International Halley Watch was presented by Louis Friedman to NASA in 1979. The intent was to maximise the scientific value of ground-based and space studies of Comet Halley. This initial suggestion met with a very positive response and has developed into a smooth organization, principally concerned with rapid communication and promoting co-operation between scientists in a wide range of disciplines. The main aim here is to put the IHW in perspective; further details of its origin and evolution can be found in Newsletter No. 1, from which the following three diagrams are taken: To quote from Newsletter No. 1 ‘The most important elements in the IHW are the Professional Observers and the Discipline Specialist Teams. Without the Observers, there can be no Halley Watch, and without the Discipline Specialists, there would be no co-ordination of observations.’ If there are any professional observers who have not yet been contacted by a Discipline Specialist it is recommended that they make their interest known immediately.