For some years now, there have been suggestions that the nuclei of planetary nebulae are stars undergoing a final gravitational contraction to the white dwarf state. These have culminated in two important studies by O’Dell, and by Seaton and his collaborators, the results of which are indicated on the Hertzsprung-Russell diagram of Figure 1. The temperatures and the distances—and hence luminosities—of the central stars are obtained from flux observations of the stars themselves and the surrounding nebular shells, the former by the Zanstra method, and the latter by that of Shklovsky.

The temporal behaviour of Rayleigh-Benard convection has attracted considerable attention in recent years, both from an experimental and theoretical point of view. Experiments (eg. Gollub and Benson 1980) have demonstrated a complicated array of non-linear behaviour, as well as the need for a model which will at least qualitatively describe what is observed.

While Uhuru’s contribution to X-ray astronomy in the energy range 1 – 20 keV (and more particularly 2 – 10 keV) has been most impressive, it remains true that satellite observations outside this energy range, and particularly at energies above 20 keV which are also accessible to balloon-borne instrumentation, have been somewhat disappointing. We cannot forsee any likely marked improvement in this situation for at least four years and we believe therefore, that balloon-borne payloads can continue to contribute significantly to the study of hard X-ray sources.

One of the quantities usually required when solving the equation of radiative transfer is the intensity of radiation emerging from the surface of the medium under consideration. For multi-dimensional situations however, the methods presented to date have been numerical, and these first calculate the so-called source function Sv (r, Ω) as a function of position r, angle Ω and frequency v. This is generally the most difficult part of the exercise since an integro-difierential equation must be solved. The emergent intensity is then determined by solving a relatively simple first order differential equation by any of the well known numerical integration schemes. However, if the emergent intensity is required at a large number of angles, frequencies, and positions on the surface of the medium, and this is usually the case, the amount of computing needed may be considerable.

Towards the end of February 1968 the astronomical world was staggered by a paper from the Milliard Radio Observatory at Cambridge announcing the discovery of an astonishing periodic phenomenon. The characteristics of the pulsating radio source—or pulsar as it came to be called—involved a fantastic multiplicity of time-scales. The duration of the individual events was measured in tens of milliseconds, the repetition rate was of the order of a second, the pulse amplitude showed drastic variations over times of seconds, minutes, hours and even months and, lastly, the stability of the basic periodicity indicated a time-scale of millions of years. A series of pulses from CP 1919, the first pulsar, is shown in Figure 1, and one notices here both the regularity of the pulses and the variation in their amplitude with time. When the individual pulses were observed on an expanded time-scale it was found that the pulses were made up of sub-pulses (Figure 2) and that there was considerable structure even down to a millisecond time-scale.

A graphical format has been adopted to depict some characteristic variations associated with the solar activity cycle up to 1988, for both the Zurich annual and monthly mean values over the respective periods from 1700 and 1750. Both low pass and band pass filtering techniques have been employed to smooth the data, the autocorrelation coefficients determined for a high number of lags to illustrate the secular modulation of the maximum values in each cycle and the spectral amplitudes computed to establish periodicities in the chronologies.

The observation of the X-ray sky from balloons, rockets, and satellites has led to the discovery of more than 100 X-ray sources. Optical and radio identifications have been made for about a dozen of these. A few X-ray sources are of extra-galactic origin, but the majority are objects in the Galaxy.

The grating ring response of the Molonglo Observatory Synthesis Telescope can be reduced by the installation of 60° phase switches into each of 176 signal paths of the antenna. A suitable voltage-controlled UHF phase switch has been designed and tested at 843 MHz. It consists of two varactor diodes in series with a microstrip. Although designed to provide only two phase states, the device works well as a continuous phase shifter with a coefficient of ∼3° per volt. Details of the design, performance and application to the radio telescope are given.

This paper presents results of CCD observations of DR Tau which show emission line variability.

Pulsar observations will be made with two new general-purpose transit radiotelescopes at present being built near Hobart.

It has been often suggested that the solar granulation is essentially a turbulent convective phenomenon. It is then worthwhile to investigate steady state, finite-amplitude convection in the outer layers of the solar convection zone. On the basis that the convection zone is turbulent, we will define an eddy viscosity; and for the present we will consider only the first 300 km of the convection zone. This value is predicted by van der Borght using an asymptotic analysis of convection at high Rayleigh number—provided we assume the horizontal dimension of the cellular pattern to be ˜1000 km.

When two stars are in orbit about each other, tidal forces cause an exchange of energy and angular momentum between the orbital motion and the fluid motion of each star about its own centre of mass. The orbit is progressively altered, and one or both stars may be catastrophically disrupted.

An experiment has been developed in order to map the submillimetre Galactic emission at four different wavelengths between 400 μm and 2 mm at an angular scale of 1°. A binocular telescope system has been realised by means of two off-axis wobbling parabolic mirrors, each one coupled to a two-channel 3He photometer. A first run of observations from Dome C is planned for the Antarctic summer 1995–96.

Using a network of ground-based stations stretching from Lae, New Guinea, to the Antarctic, and high altitude balloons and rockets, the Hobart cosmic ray group is studying several aspects of naturally-occurring high energy radiation.

Observations of the large-scale organisation of matter in the Universe are of great importance in present day astronomy. In the visible part of the spectrum such observations are mainly of the distribution of galaxies on the plane of the sky.

Direct and objective prism plates obtained using large Schmidt telescopes form the bulk of the material used. The direct plates provide the observations from which the surface distribution of galaxies may be determined and the prism plates and FLAIR, via redshifts, yield extragalactic distances and hence the three dimensional distribution of galaxies.

For large-scale surveys the measuring machines used need to be multi-purpose and fast such as COSMOS and SUPER-COSMOS at the Royal Observatory Edinburgh. More specific programs can make use of smaller, slower machines such as iris photometers and microdensitometers.

The method of analysing the data produced rely on seeking density enhancements in the general field of galaxies for cluster detection or using correlation techniques for analysis of the galaxy distribution.

A description is given of a southern sky catalogue containing 109 objects recently completed and an outline of some of the extragalactic projects underway using this large body of data.

The distribution of faint galaxies in a deep sample, down to a limiting magnitude of B ~ 21.5 in a region of some 30 square degrees of sky at the South Galactic Pole, is investigated. The sample was obtained from objective measurements made with the COSMOS automatic plate-scanning machine. The two-point angular correlation function shows positive correlation on scales out to ~1.5° and thereafter positive correlations on scales ~ 2.5° and ~ 5° indicating the presence of clustering in this sample on linear scales out to ~ 8h-1 Mpc and at ~ 13h-1 and ~ 27h-1 Mpc. On application of an algorithm for the detection of filamentary structure in the distribution of the galaxies, a negative result is obtained.

Mid-infrared spectroscopic data on SN 1987A are reviewed. This spectral region contains the fine structure lines of a number of ions, incuding the iron group elements, together with recombination lines of hydrogen and helium. From about 9 months all these lines and the continuum have been effectively optically thin, and the [CoII] line strength and development yields an estimate of the parental 56Ni mass of 0.071 M⊙, very similar to the light curve estimates. At one year after the explosion the velocities appropriate to the hydrogenic and ionic regions are ∼ 2000 km s−1 and ∼ 1500 km s−1, respectively.

Apart from an excess between 8–9 μm which appears to be due to molecular SiO, there is no evidence of departure of the continuum from free-free emission, and no sign of any emission from dust. From the free-free continuum an ionization fraction of a few percent is derived for the hydrogen/helium envelope; this provides relative transparency in the mid infrared while the bound electrons provide the X and γ-ray opacity which is still considerable at 15 months.

The appearance of neutral ions at 15 months indicates that the ejecta temperatures are cooling, and that dust formation may be imminent.