The resistive tearing mode instability is a mechanism that in some cases will render unstable a magnetohydrodynamic equilibrium of a plasma that is ideally stable, i.e. stable if no dissipative oiesses are taken into account. There is much experimental evidence that this instability is the cause of the current disruptions observed in laboratory plasma devices (von Goeler et al. 1974). In the astrophysical context, the instability has been invoked in connection with the solar flare energy release mechanism (Coppi and Friedland 1971) and the problem of the disconnection of the protostar matter from the interstellar magnetic field during star formation (Mestel 1966). In the latter problem the tearing instability gives rise to a much smaller timescale for magnetic reconnection than does ordinary resistive diffusion.

The complex flare related events taking place in the solar corona are becoming better understood as more observations are made with high spatial and temporal resolution nearly simultaneously at widely separated radio frequencies. Similarly the magneto-plasma structures related to the so-called quiet Sun, which have been extensively studied during the recent cycle (No. 20), are now better understood because of such high resolution observations.

The β Cep variables are characterised by light variations of a few per cent and velocity variations of up to a few tens of km/s over periods of from about 2.5 to 7 hours. Spectral types range from BO to B2 and luminosity classes from IV to II-III, corresponding to masses from 8 to 18 M ⊙. The light and velocity curves are 90° out of phase, so that maximum light (and also maximum temperature) occur at minimum radius.

In recent years observations of γ-ray emission from the disk of the galaxy have provided a new opportunity for research into the structure of the spiral arms of our own galaxy. In Figure 1 we show a map of the structure of the disk of the galaxy as observed for γ-rays of energy > 100 MeV by the SAS-2 satellite (Fichtel et al. 1975). The angular resolution of these measurements is ~ 3°, and besides two point sources at l = 190° and 265° several features related to the spiral structure of the galaxy are evident in the data. Most of these γ-rays are believed to arise from the decay of π° mesons produced by the nuclear interactions of cosmic rays (mostly protons) with the ambient interstellar gas. As a result, the γ-ray fluxes represent a measure of the line of sight integral of the product of the cosmic ray density N CR and the interstellar matter density N 1

It is likely that in most stars certain layers, either in the interior or outer regions, will be unstable against convection and the study of energy transport by convection has raised considerable interest since the early days of this century when Karl Schwarzschild derived his criterion for deciding whether a certain region is in convective or radiative equilibrium.

In this paper we summarize the results of radio studies of the distribution functions (number, energy distribution and pitch angle distribution) of the energetic particles that are produced at the time of solar flares. We consider the clues and constraints they impose on the mechanisms of acceleration, bearing in mind that radio evidence implies that there are at least two stages of acceleration in many flares.

In the following sections we discuss the distribution functions of the particles resulting from (a) first phase acceleration, (b) first and/or second phase and (c) second phase acceleration. Table I summarizes the results.

A major requirement of modern radio astronomy is the attainment of the highest possible angular resolution. This high angular resolution should be matched by a high sensitivity and by spectral and polarization capabilities. Study and experience have shown that no form of telescope is more effective in this respect than the aperture synthesis type. The past few years have seen a growing realization amongst astronomers, both here and overseas, of the need for a new synthesis telescope able to observe the full southern sky. This realization has been stimulated by several factors:

The visual spectra of some hot stars, including P Cygni, have emission with associated absorption troughs ˜ 102 km s-1 on the short-wavelength side (Beals 1929, 1951). These P Cygni profiles are easily understood in terms of mass flowing away from the star. Later, rocket observations of the far-ultraviolet resonance lines (Morton 1967) showed that the phenomenon is rather common among hot stars and the velocity shifts could be from 1000 to 3000 km s-1, demonstrating that the mass must be escaping from the star. Resonance lines provide the strongest absorption in the shell where neither the density nor the radiation field is high enough to leave many ions in excited states. Since the ion stages likely to be present around a hot star have their resonance lines shortward of the atmospheric cutoff, space observations are essential in this investigation. Figure 1 shows the P Cygni profile of O VI in ς Pup obtained with Copernicus satellite spectrometer.

At previous meetings of the A.S.A., brief reports have been made of a new theory for the formation of the solar system which is being developed at Monash University (Prentice 1972, 1977, 1978a, b; Hourigan 1977). This work is nearing completion and on this occasion an outline of the whole theory is presented.

It has generally been accepted that moving type IV bursts are generated as synchrotron radiation from energetic electrons high in the solar corona (Boischot and Denisse 1957). At 80 MHz the peak brightness temperature is usually ~ 108 K and the radiation becomes highly circularly polarized as the burst decays. This has led several authors (Kai 1969; Dulk 1970, 1973; Schmahl 1972; Robinson 1974, 1977; Nelson 1977) to the conclusion that the radiation comes from mildly relativistic (~ 100 keV) electrons and occurs at low harmonics of the gyro-frequency (gyro-synchrotron radiation). We present evidence of moving type IV bursts at 43, 80 and 160 MHz with brightness temperatures of ~ 109 K, and one at 43 MHz as high as 1010 K. The number (~ 1033) of energetic (≥ 1 MeV) electrons which is required in order to explain such high brightness temperatures by incoherent gyro-synchrotron emission is very large and near the upper limit for the number of fast electrons accelerated in the second phase of a solar flare. If amplification takes place a smaller number of electrons with energies ~ 100 keV would be required.

The basic model for the precipitation of trapped energetic particles from a magnetic flux tube is Kennel and Petschek’s (1966) model. Their model is symmetric, implying equal precipitation rates at the two feet of the flux tube. We have developed a model for precipitation in an asymmetric flux tube (Melrose and White 1979). Here we explore some of the consequences for the precipitation model of Melrose and Brown (1976) for solar hard X-ray bursts. In Melrose and Brown’s model roughly half the X-rays arise from precipitating electrons. With present instruments it is not possible to resolve the two feet of the flux tube. However, if the feet can be resolved, either directly by future X-ray telescopes, or indirectly through secondary optical, UV or radio observations, then, as we shall show, the additional information obtained could be used to derive information on processes in the magnetic trap.

Whether a mechanism for the emission of radiation can properly be regarded as thermal or non-thermal depends on the nature and extent of the interactions that take place between the radiation resulting from such a process and the surrounding medium. Thus, no matter what the emission mechanism there can be a balance between emission and absorption processes such as to produce a state of local thermodynamic equilibrium (LTE), so that the net radiation available for transport through the source region is thermal.

The Culgoora radioheliograph was designed in the early 1960s and commissioned in 1967. Since then there have been dramatic increases in the speed and versatility of digital integrated-circuit devices, and also a marked fall in their cost. It is now possible to replace the original signal processing electronics with equipment, based on modern digital technology, which will significantly enhance the performance of this radio telescope for solar and cosmic radio observations at metre wavelengths.

One of the important discoveries of the present century is that the Universe expands. Two important parameters which define the dynamics of the Universe and can be obtained at the telescope are the rate of expansion zhqо, and change of this rate with time qо, It is difficult to derive a value for Hо because accurate distances of farther galaxies are needed. This involves identifying the luminous objects, such as brightest stars, HII regions, globular cluster, supernova etc., in the Local Group galaxies as well as in the external galaxies. Once the absolute magnitudes of these objects are calibrated with the known distances of the Local Group galaxies, distances to the external galaxies can be derived.

At the first A.S.A. meeting in 1966 radio astronomers knew of only the 21 cm line of hydrogen, a handful of hydroxyl lines and some radio recombination lines. The number of molecular lines now known in the radio spectrum is close to 220, so radio spectroscopy has become a fully fledged subject. I shall not discuss here the recent ultraviolet studies of H2, HD and CO molecules that have been reviewed by Spitzer and Jenkins (1975).

Infrared astronomical observations using ground-based equipment are confined to the few ‘windows’ or observation ports allowed by our absorbing atmosphere, the chief absorbing molecules being water vapour and CO2. The majority of such observations have been made using broadband filters defining the photometric J, H, K, L, M, N and O bands. Some narrow band and spectral work (essentially all photometric) has also been carried out, particularly in the 8-14 micron window. From a very few high altitude, cold, dry sites (where the integrated water vapour content of the atmosphere above the site is consistently less than 1mm), it is possible to make observations at 35 and 345 microns. In Australia, the integrated water vapour content above us is typically 15 mm, only rarely dropping below 7 mm, so that long wavelength IR measurements simply cannot be made using ground-based instruments in Australia. Water vapour is fortunately not well mixed in our atmosphere and by raising our observational platform to a high enough altitude we can in fact achieve quite high transmission for all wavelengths from 10 microns to 1 mm, where we link up with microwave observations using essentially radio techniques.

Pulsars are unique astronomical objects in that their emission is in the form of a periodic pulse train. For most pulsars the pulse duty cycle is small, only a few per cent of the period. The shapes and intensities of individual pulses are in general quite variable. This is illustrated in Figure 1 which shows a series of individual pulses from PSR 1133 + 16. Despite this variation in shape of individual pulses, it is found that the mean or integrated pulse profile obtained by adding many pulses synchronously with the period is in most cases stable in shape.

Studies of coronal transients observed in white-light (Gosling et al., 1976) have shown that fast-moving events (≤ 400 km s-1) are closely associated with flares and with type II and IV radio bursts while slow-moving events are not. We now report the first detection of the radio counterpart of a slow-moving transient. The event of 1974 January 21 is shown to be visible on maps of the quiet Sun made at a frequency of 80 MHz.

Since the discovery of variable circular and linear polarisation in VV Puppis (Tapia 1977), several investigators have observed the system. The new observations particularly of polarisation (Liebert et al. 1978, Liebert and Stockman 1979 have ruled out the standard dwarf nova (accretion disc — hot spot) model previously used to interpret the light curve of VV Puppis.

I shall briefly outline some observational aspects of the Magellanic Stream before discussing the pros and cons of the two conflicting theories of its origin: a) that the Stream was pulled out of the Clouds by tidal forces produced by a close encounter with our Galaxy and b) that the gas clouds of the Stream are primordial and in the same orbit as theMagellanic Clouds.