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 the Magellanic Clouds.

The UK 1.2 metre Schmidt Telescope came into operation in 1973 with the primary purpose of extending to southern declinations the Sky Survey carried out with the Palomar 1.2 metre (48 inch) Schmidt Telescope. This telescope is, in most respects, an exact copy of the Palomar telescope, but several recent developments result in a much fainter limiting magnitude (by about 2 magnitudes) for the Southern Survey. The UK Schmidt Telescope has an aperture of 1.2m, and the spherical primary has a diameter of 1.83m and focal length 3.07m. The plates have the dimensions 356 x 356mm, giving a field of view of 61/2°; the plate scale is 67″ 1/mm.

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.

In this paper we review the evidence on the structure of the open magnetic field lines that emerge from solar active regions into interplanetary space. The evidence comes mainly from the measured sizes, positions and polarization of Type III and Type V bursts, and from electron streams observed from space. We find that the observations are best interpreted in terms of a strongly-diverging field topology, with the open field lines filling a cone of angle ~60°.

It is impossible in half an hour to do justice to the vast literature on Shockwaves in interstellar space. Here, an attempt is made to identify outstanding problems with particular regard to the optical spectrum and to determine what physical data can be relatively unambiguously obtained from interpretation of this.

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.

Many authors (e.g. Magun et al. 1975) have debated the question ‘does solar type IV continuum emission arise through Langmuir wave conversion or through gyro-synchrotron emission?’ Culgoora radio spectrograph and heliograph observations of the late stages of a recent (7 September 1977) type II, IV event showed both type IV* (continuum) and transient type III (electron-beam) emission coming from the same source, high above the solar limb. These observations suggest that this particular type IV continuum arose through a mechanism similar to that of the type III, probably fundamental Langmuir-wave emission, in a corona with a tenfold enhancement of plasma density.

The standard formula for the resolving power R(= λ/Δλ) of an astronomical grating spectrograph is Here L is the linear size of the grating, perpendicular to the direction of the grooves, θB is the blaze angle of the grating, θS is the angular size of the slit, projected back on to the sky, and D is the diameter of the telescope objective. The formula is valid for gratings used in the Littrow condition, when the angle of incidence α, and the angle of diffraction β, are both close to θB.

The Thumbprint Nebula (TPN) in Chamaeleon (first described by Fitzgerald (1974), and shown in Figure 1) is a good example of the class of dense, dark nebulae that exhibit dark cores and bright rims, and have been referred to (Lynds 1967) as ‘bright dark nebulae’. Early observations of these nebulae established that the dust grains within them were strongly forward-scattering (Struve and Elvey 1936, Struve 1937). However, the treatment of the radiative transfer problem was too inadequate to permit more than tentative conclusions regarding the nebulae. In more recent years, with the advent of modern computers, the transfer of radiation through a dust cloud has been treated more rigorously, using Monte Carlo techniques (Mattila 1970, Witt and Stephens 1974). Witt and Stephens (1974) have demonstrated that for a dense nebula the surface brightness profile is sensitive to the dust grain density distribution within the cloud and to the scattering properties of the grains. The scattering model approach can be valuable in the investigation of very opaque dark nebulae that cannot be studied by conventional star counting techniques. This has been demonstrated in the case of the TPN by Fitzgerald et al (1976), who used the Witt and Stephens model.

In this talk I shall describe briefly some of the theoretical ideas of the origin of the Magellanic Stream and then give a more personal view of the results of model fitting.

The Magellanic Stream definitely seems to be an extragalactic feature: the apparent connection of the Stream to the Magellanic Clouds and the continuity of the radial velocity profiles make it highly implausible that the Stream is a local foreground feature.

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.

About 20 years ago de Vaucouleurs (1955, 1960) drew attention to faint but extensive nebulosity in the region of the South Celestial Pole. He tentatively identified it as being emission nebulosity, excited by OB stars in the overlying galactic plane. The extent of these nebulae has become even more apparent in recent years on IIIa-J plates taken for the U.K. Schmidt survey of the southern sky. From a study of survey plates covering the sky south of declination 80° a map has been prepared of the nebulosity visible in the region. A study made of this ∽nebulosity suggests that it is predominantly reflection nebulosity, with the main source of illumination being integrated starlight of the overlying Carina spiral arm. The bulk of it is of very low surface brightness (fainter than about 26 mag. per square arcsec) and appears to be in the form of a broken layer underlying the local galactic plane at an altitude of ∽ 40–80 pc. There are a number of brighter nebulous patches and filaments, frequently highly structured on a scale of minutes of arc, and extending across several degrees, usually parallel to the galactic plane.

The proposal made to ASTEC for an Australian systhesis telescope (AST) is for a high-sensitivity, high-resolution synthesis array to be located at the Australian National Radio Astronomy Observatory, Parkes, and used in conjunction with the existing 64-m antenna at that site as a national facility (Wellington 1976). During the past 18 months a design study group consisting of representatives from the Australian National University, University of Sydney, University of Tasmania and CSIRO has been investigating the design of such an array. This paper reports on one aspect of this design, the array configuration.

Most if not all metre-wave Type III bursts appear to be associated with solar active regions (e.g. Duncan 1977). There is a well-known association of Type III bursts and flares within a few minutes of the onset of the brightenings seen in Hα (Wild et al. 1954). Early descriptions of these observations were given by Malville (1961) (or see Kundu (1965) for review). More recently Jackson et al. (1978) have reported the occurrence of a broad maximum of Type III bursts 10 to 5 h prior to mass ejection transients seen by the white light coronagraph on Skylab.

Observations of the distribution of millimetre-wavelength brightness over the quiet Sun provide an important test of models of the solar chromosphere. The author and colleagues have recently carried out two investigations of the quiet-Sun brightness at 3 mm wavelength — one by means of a total eclipse observation (Labrum et al. 1978) and the other by aperture synthesis with a two-element interferometer (Archer et al. 1978). I present here a preliminary discussion of these and other measurements of millimetre-wavelength brightness distributions and of their interpretation in terms of chromospheric structure.

The history and achievements of interferometric angular diameter measurements have been reviewed recently by Hanbury Brown (1974) and only a brief outline will be given here. As the title is intended to imply, the present discussion will be limited to interferometry involving baselines in excess of telescope aperture diameters.

In this paper, two models for the origin of modulation lanes in Jovian radiation are discussed. The results of calculations of dynamic spectra due to the Cotton-Mouton effect in Jupiter’s plasma envelope and due to modulation of the frequency spectrum in the source are reproduced. The characteristics of the theoretical spectra are then described. This offers the possibility of solving the problem of modulation lanes by comparison of observed Jovian dynamic spectra with the theoretical ones.

We compare observations of a large coronal streamer made with the 80 MHz Culgoora radioheliograph, the Kcoronameter on Mauna Loa and the white light coronagraph on Skylab. The various measurements are not in agreement, and this raises fundamental questions about the nature of the corona and wave propagation through a streamer structure. The comparisons also indicate how precise data from the heliograph may contribute to a better understanding of these processes.

The major programs at the Molonglo Radio Observatory are nearing completion. Much can still be done using the existing 1 mile Cross-type radio-telescope (Mills et al. 1963) but, to tackle properly many of the current problems in radio astronomy, a fundamental change is required from a transit to a trackable radio-telescope, combined with an increase in the operating frequency and the resolution.

The spectrophotometric results from the Copernicus satellite have stimulated considerable interest in interstellar molecular hydrogen. In this note calculations are presented which suggest that it may be possible for hydrogen molecules on grains to give rise to diffuse interstellar lines in the ultraviolet.