Extensive air showers radiate because they are essentially sheets of charge moving through a medium at relativistic velocities. Of interest in the present experiment are their emissions in the optical and radio regions of the spectrum—the first long accepted as primarily of a Cerenkov origin, and the second very far from fully understood.

The cold HI cloud in the region of the M17SW giant molecular cloud comprises three major fragments with a mean size of ~ 30 pc. Their overall distribution is rather similar to that of CO gas, but one of the fragments does not seem to have a molecular counterpart. It is shown that such a cloud is also a future site of star formation.

The initial results of a southern sky survey of the peculiar velocities of 1355 spiral galaxies by a group at Mount Stromlo and Siding Spring Observatories (MSSSO) are discussed against the background of past work in this area. The most important result is that the Great Attractor does not exist; rather, there is bulk flow relative to the cosmic microwave background (CMB) of amplitude 600 km s−1 and scale greater than 130 h−1 Mpc in the Supergalactic plane. This is generated by the assumption that the CMB dipole is Doppler induced by our Galaxy moving at 622 km s−1 relative to the CMB. This may be incorrect, in which case there is no bulk flow and the radiation dipole is cosmological in origin with important implications for the early Universe.

During 1968 we have found at Parkes several types of emission in the lines of the 18 cm quadruplet of the ground-state OH molecule. This note describes a strong source of 1612 MHz emission near galactic longitude 331°.

OH emission was originally detected in the vicinity of HII regions, and a search of a large number of HII regions showed that about a third had associated OH emission. This type of emission is usually strongest at 1665 MHz, and is also seen at 1667 MHz and weakly on one of the satellite lines.

The two important parameters which essentially determine the nature of the convective regime, and consequently the total heat transported by convective processes, across an unstable layer in a star are the Rayleigh and Prandtl numbers defined by (Chandrasekhar 1961)

where ν is the coefficient of kinematic viscosity, x is the coefficient of thermal diffusivity and α, g, d, ΔT are respectively the coefficient of thermal expansion, acceleration due to gravity, depth of the fluid layer and temperature difference across the layer. In addition, the horizontal scale of the convection cell is determined by the horizontal wave number a and for convection to be established R must be greater than the critical value at marginal stability, Rc , which is a function of a, given by

when the free boundary conditions apply.

The Magellanic Clouds are the nearest major extragalactic objects to the Milky Way. The study of young giants or supergiants in the Clouds enables us to obtain information regarding the birth rates and evolution of young massive stars in those systems, free from biases inherent in similar studies in the Galaxy. Although the Magellanic Clouds have been studied by an extremely large number of research workers at optical wavelengths, it is only recently that significant infrared observations have also been undertaken (e.g., Glass 1979, McGregor and Hyland 1981, Cohen et al. 1982). Cool supergiants in the SMC have been studied optically by Humphreys (1979). She found that most are very metal deficient, and should be classified spectroscopically as M0.

In this paper the relation between the planetary distance law and the resonant structures is shown, in that the resonance relation has been expressed in terms of Roche’s constant (Rawal 1984,1986,1989). This brings forth a coherent, elegant and unified picture of the Solar System and satellite systems.

Regions of the interplanetary medium currently inaccessible to space vehicles may conveniently be studied using the radio scattering properties of the interplanetary plasma. These effects may give rise to angular broadening of radio sources sufficiently close to the Sun, or to amplitude scintillation of sources of small angular size.

A model is explored for energy release in solar flares that involves a constant coronal current. An emerging flux tube is assumed to carry a current I≲1012 A, and this current is assumed not to change during flare. Using a circuit model, explosive energy release is attributed to a rapid rise in the coronal resistance R c, which must adjust to R c = − L c, with L c the rate of change of the coronal inductance L c, to ensure I = constant. In this model the total energy released in the corona is twice the change in the magnetic energy stored in the corona. It is argued that this energy is inadequate to power a large flare and the implications of this conclusion are discussed.

In this paper we obtain an approximate expression for the temperature structure of a stellar atmosphere heated by an external flux of soft X-rays. Allowance is made for reradiation in both the soft X-ray and optical regions. As may be expected our results indicate that the temperature structure will be drastically changed from the grey T-T relation, particularly at low optical depths. The stronger lines should appear in emission with the possibility of a central absorption in certain circumstances. The present results are in general agreement with those of Strittmatter (1974).

Over the last two decades there has been an accumulation of exciting evidence that appears to show that, as early as 5000 years ago, people in Britain were making precise observations of the Sun, Moon, and stars, and studying small perturbations in the lunar motion. Structures such as Stonehenge, and the s thousands of other megalithic sites in Britain, are then seen as prehistoric observations. Within these, data would be (accumulated to enable the prediction of celestial phenomena such as eclipses, and allow the construction of a calendar. Recently however a small number of rigorous statistical studies of the sites have cast doubt on the astronomical hypotheses, and have posed the question of whether some of the support for these hypotheses has been generated by well-intentioned but over-enthusiastic selections of chance alignments. In this review, the arguments and counter arguments are presented and examined, and we see what can be salvaged from the astronomical hypotheses after the statistical smoke has cleared.

Recent laboratory experiments have confirmed theoretical expectations that the aligned rotator model (Goldreich and Julian 1969) does not function in the way originally expected, if at all. These experiments confirm that the nonneutral (completely charge-separated) plasma is isolated into finite regions, which in the case of the magnetosphere about an aligned rotator means in general that there is no plasma from the neutron star to be found at the light-cylinder. Hence the interesting pulsar-like properties originally postulated no longer follow.

The traditional approach to the extragalactic distance scale rests on a pyramid of primary, secondary and tertiary indicators of increasing range and decreasing accuracy. Thismulti-step procedure, fraught with the danger of cumulative errors, has led in recent years to two main, widely diverging scales: the ‘long’ scale (Sandage and Tammann 1974, 1975, 1976) implying a Hubble constant and the ‘short’ scale (de Vaucouleurs 1978, 1979; de Vaucouleurs and Bollinger 1979; de Vaucouleurs and Peters 1981; de Vaucouleurs et al. 1981) leading to H 0 ≃ 100. Several authors have already shown that the long scale rests on very precarious foundations (Capaccioli and Fasano 1980, de Vaucouleurs 1981, Hanes 1980); counter arguments have been offered in its defence and to criticize the short scale (Tammann, Sandage and Yahil 1979, Sandage and Tammann 1982). For want of a conclusive test a consensus was still lacking.

This review is concerned mainly with the solar modulation of galactic cosmic rays and the progress that has been made since the Tenth International Conference on Cosmic Rays (Calgary, June 1967), My aim is to set out some of the advances in the basic theories; to indicate why certain disagreements between convection-diffusion theory and observations (noted in Webber’s invited review at Calgary) are to be expected; and to indicate some of the currently emerging areas of interest.

We give an account of the life and work of William James, including his many contributions to astronomy in Australia mainly through his skill in designing, figuring and testing aspheric surfaces.

Clusters containing cepheids, and especially clusters containing more than one cepheid, provide information on the advanced evolutionary stages of massive stars, and on the factors which influence the period-frequency relations and lifetimes of cepheids. NGC 1866, in the LMC, is already well known in this respect. NGC 2010 was found by Hodge to contain two cepheids. Two more variables have been found in this cluster which, from their magnitudes and colours, are almost certainly cepheids, though we do not yet have periods for them. We noticed also that two known cepheids, HV 2868 and HV 2870, are associated with NGC 2136.

The problem of the surface migration of solar magnetic fields is discussed. It is shown that, unless some form of reconnection takes place below the surface, magnetic tension should effectively prevent such migration and the possibility of U-loop formation and transport is considered. As a first step, the buoyancy of a magnetic ‘U-loop’ within an isothermal atmosphere is considered. It is shown that such a configuration may form by the reconnection of the arms of an Ω-loop associated with an active region, and is likely to be buoyant initially and rise through the region. However, as it rises, the net buoyancy decreases and, provided that the temperature within the loop is even marginally less than that outside, it will reach a sub-surface configuration in which the net buoyancy is zero. The significance of this result for solar magnetic fields is then assessed.

Until comparatively recently solar activity was discussed in terms of independent centres around the Sun’s surface. These centres, which form a constantly but slowly changing pattern, were thought to be linked only beneath the photosphere by tangled magnetic fields, themselves dominated by the mechanical energy of mass motions at photospheric and lower levels. Recent discoveries now indicate that active centres interact with one another above photospheric level and especially through linkages within the corona. The linkages appear to be of at least two distinctive kinds: magneto-hydrodynamic shock waves capable of travelling vast distances through the corona at ∼103 km/s and triggering eruptions at distant centres; and magnetic field lines which loop high and wide in the corona and convey energy in the form of fast particles. These two kinds of interaction will be considered in turn.