The discoveries made by the Voyager 2 spacecraft at Uranus in January 1986 are discussed in the light of the modern Laplacian theory for the formation of the solar system. Various accounts of this theory, which has as its basis the concept of supersonic convective turbulence, have been presented at previous meetings of the ASA (Prentice 1977, 1979, 1981a). The most important confirmation by Voyager was the discovery of 2 new satellite groups near orbital radii 2½ RU and 3½ RU (RU = Uranus’ equatorial radius = 26, 200 km), as first predicted in 1977. The discovery that the densities of the Uranian satellites are consistent with these bodies having condensed in a single compositional class, consisting of anhydrous rock, NH3 ice and CH4.6H2O clathrate hydrate in normal solar proportions, confirms the hypothesis that the chemistry of all planetary/regular satellite systems are accounted for by a single choice of the turbulence parameter, namely β = 0.107 ±0.001. The implication of the Voyager data for the origin of comets is also discussed.

The geographic South Pole, where the United States maintains a year-round scientific station, affords a number of unique advantages for certain types of astronomical observations. These include: continuous viewing and constant declination of ail objects in the southern celestial hemisphere, exceedingly low humidity, extended periods of coronal seeing, high altitude, and uniform terrain. The areas of research that have already benefited immensely from thèse extraordinary features are helioseismology and submillimeter astronomy. Unparalleled observations of global solar oscillations have already yielded significant information about the structure and dynamics of the Sun’s interior. Far infrared measurements of various galactic and extra-galactic regions have attained an unprecedented level of sensitivity, limited for the first time only by the noise inherent in the detector. In addition to further helioseismological observations, currently planned future activities include observational cosmology and ultra high energy gamma ray astronomy.

Reported data on the Chandlerian nutation show that there are irregular yet related changes in the rate of energy gain, the damping and the phase, changes which were remarkably great in the late 1920s. Dynamical interpretations need a model that has friction elements as well as springs and dashpots; it then offers further applications as well; e.g. to a correlation between reported values of the Love number k and tidal potentials. The model is used in discussing the increases in amplitude and the advances in phase; the short and long-term rates of energy gain and their interruptions and damping; the correlation between short Chandlerian periods and large amplitudes in the annual nutation; and the correlation between damping and the apparent frequency. Doubts are expressed about nutational values of Q. A geophysical interpretation of the model is obtained from seismic data. It was found that every large rise in the nutational energy was preceded by an earthquake in the Andes region; and that the secular rate of energy gain varied with the circum-Pacific seismicity. Decreases in these were accompanied by rises in the Earth’s rotational acceleration and were followed by deep earthquakes in a diminishing region east of the Andes. It appears that the nutational and seismic events are due to tectonic stress, and intermittently this is relieved by subduction.

Henry Abraham died on 9 December 1985. A few days earlier, he explained to me the work he had been doing in recent years, and gave me responsibility for his documents and notes. Amongst them were the manuscript for the above paper, prepared about 1979 but not submitted for publication then, and meticulous and extensive notes which examine further the questions raised by the paper. It has seemed to me to be appropriate to submit for publication the above paper as he wrote it, and to add a summary of his subsequent work as I interpret it.

A review is presented of the evidence for anisotropies of galactic origin in the charged cosmic ray particle intensity at median primary energies of detection in the range 1011 – 1014eV. It concerns the period from 1958, when the first substantial long-term observations at energies of solar and sidereal modulation near 1011eV commenced underground, until 1984, by which time results were available from a number of years of accurate observations with detectors of small air showers at energies near 1014eV, too high for complicating effects of solar origin to be present. There is evidence for the existence of both unidirectional and bidirectional galactic anisotropies over the whole energy range. Tentative descriptive models are discussed in relation to advances both in solar and sidereal analytical techniques and in the ability of experimenters to account for and exploit the modulating influence of the heliomagnetosphere at the lower energies of detection.

Visual meteors, due to impinging meteoroids of radius about 1 cm, appear at a rate of a few per hour during non-shower periods. Smaller meteoroids (100 μm – 1 cm) give rise to less bright trails, but are much more abundant. These are usually detected by radars of about 10 m wavelength which, over the past 40 years, have produced a plethora of information concerning mass and height distributions, orbits, etc.

Using such ‘conventional radars’, the peak of the measured height distribution is found at about 95 km, with few meteors detected above 105 km. However, the flux detected is only a few percent of the total flux (a) measured using a large (10 m) optical collector, and (b) expected from a comparison with measurements by satellite impacts and zodiacal light observations (radii < 100 μm). One possibility is that the radars detect few low-velocity (V < ~25 km s-1) meteors since these produce little ionization and thus limit their detectability: the ionizing efficiency of meteors varies as ~ V7/2. In direct opposition, our alternative hypothesis is that the undetected flux is held in a faint high-velocity component which ablates at high altitude. These are not detected by conventional radars because meteor trails have ‘initial widths’ of about 3 m at 105 km; for a radar wavelength of 10 m, components scattered from different regions of the trail therefore destructively interfere, and the probability of detecting any meteor above 105 km is small.

In order to test our hypothesis we have measured the height distribution with a 150 m radar, and we are commencing ancillary observations at 50 m; compared to these wavelengths the initial width is small to at least 140 km. The results show a peak at 105 km with most meteors being above this, significant numbers occurring right up to 140 km. This suggests that the true flux is at least 10 or 20 times that previously deduced, having implications for the number of cornets in the recent past and the balance of material between the smaller bodies in the solar System.

Linear stability theory for Rayleigh-Benard convection shows that for a specified Rayleigh number, greater than some critical value, only a finite range of horizontal wave numbers support convective instability in a horizontal layer of fluid heated from below. However, it is not possible to predict the preferred horizontal scale of established motions from this approach although it is clear from observations, particularly of the solar surface, that a preferred cell size does prevail. In an endeavour to establish a preferred horizontal scale appropriate non-linear modal equations have been integrated forward in time, initially incorporating a discrete band of wave numbers equally spaced across the range that supports convection, for a specific Rayleigh number. The horizontal resolution was improved in subsequent integrations by first deleting modes that had substantially decayed and then introducing new modes on a finer horizontal mesh in the vicinity of what appeared to be the evolutionary dominant mode. Finally, the multimode integrations were continued in time until the evolution of a dominant horizontal mode from within the restricted range was evident. Both the model characteristics and numerical scheme adopted placed limits on the degree of horizontal refinement that could be undertaken with confidence.

A theory for the source of free energy for the Langmuir waves producing Type II bursts is presented. It is shown that electrons accelerated at the Type II shock naturally develop a distribution function with an abrupt cutoff at a characteristic minimum parallel velocity (a ‘cutoff distribution) in a limited spatial volume ahead of the shock, irrespective of the acceleration process active at the shock. The long duration, narrow bandwidth Type II radiation is then explained in terms of Langmuir waves produced by a cutoff distribution. The theory also accounts in a natural way for split-band Type II bursts and herringbone bursts.

Many of the X-ray pulsars for which X-ray lightcurves have been presented in the literature exhibit asymmetric emission beams. We postulate the existence of an off-centre magnetic dipole field embedded in the rotating neutron star and show that such a field leads to varying rates of matter transfer between an accretion dise and the neutron star surface, over a rotation period. Assuming that the accretion rate onto the surface is simply related to the luminosity, we show that most of the observed asymmetries can be accounted for by this mechanism.

The dynamics exhibited by systems, such as galaxies, are dominated by the isolating integrals of the motion. The most common are the energy and angular momentum integrals. The motions in a system with a full complement of isolating integrals are regular, that is, periodic or quasi-periodic. Such a system is integrable. If there is a deficiency in the number of integrals, then the motions are chaotic. There is a fundamental quantative difference in the motion, depending on the number of integrals. A technique, called Generalised Painlevé analysis, based on complex variable theory allows the user to determine if a system is integrable. Two new integrable cases of the Henon-Heiles system are presented, bringing the total number of such integrable potentials to five. It is highly probable that there are no further integrable cases of the Henon-Heiles potential. Five cases of the quartic Verhulst potential, defined by certain restrictions on the coefficients, which are found to be integrable are summarised.

A particle method for the simulation of the global evolution of cold gas in galactic potentials is described. It incorporates an efficient artificial viscosity, based on the smoothed particle hydrodynamics approach, which conserves both linear and angular momenta and in the continuum limit is equivalent to a Navier-Stokes viscosity in a compressible gas. Parameters of this viscosity have been calibrated in such a way as to make a gas disk, embedded in an axisymmetric galactic potential and originally inclined to its equatorial plane, settle to the preferred plane on the time scale characterizing the differential precession. After a careful analysis of the previously published settling times we find that our results are consistent with Steiman-Cameron’s (1984) lower limits, and we argue that Simonson’s (1982) time scales have been seriously underestimated. We also demonstrate that two dimensional methods based on rigid rings do not model the evolution of a differentially precessing settling gas disk realistically and cannot be used to study the morphology of gas distribution.

Roche (1850) made the first study of the stability of binary systems. The problem he studied, and which now bears his name, is concerned with the stability of a liquid star in a synchronous, circular orbit about a point mass. Roche’s calculations predicted that if the separation between the liquid star and the point mass is S2.5rs’/3, where r is the unperturbed radius of the liquid star and s the ratio of the mass of the point to the mass of the liquid star, then the liquid star would be unstable. This result was generalised to two liquid stars orbiting each other by Darwin (1910, p. 436). Using the tensor virial method Chandrasekhar (1969) has given a uniform analysis of the classical result. The classical results have been extended by Hachisu and Eriguchi (1984a, b) who looked for the onset of instability in polytropes in binary orbits.

An HI survey of the Large Magellanic Cloud (LMC) has been reanalyzed to find the transverse velocity of the LMC, and derive an upper limit of 4.5 × 1011 M⊙ for the mass of our Galaxy out to 50 kpc. A rotation curve is derived for the LMC from the HI data giving a best mass estimate of (4.0±0.4)×109 M⊙. Velocity observations of 97 planetary nebulae (PN) in the Large Cloud are used to compare the old and young components. Our results are found to be at odds with an earlier sample of 9 old clusters, which is interpreted as being due to the low number of objects in that sample. The w-component of velocity dispersion of the PN population is 35 km s-1 and that of the HI 10 km s-1. If this difference is a result of stellar diffusion then the average age of the PN population is 1.3 × 109 yr, implying a precursor mass of 1.8 M⊙ and a remnant mass of 0.63 M⊙.

At optical wavelengths NGC 4945 is a nondescript edge-on spiral galaxy, much of which is obscured by dense dust clouds. However, at longer wavelengths a prominent nucleus is exposed which possesses both Seyfert and star-burst characteristics. Microwave observations highlight dense molecular clouds located near the nucleus. The large velocity range of these clouds lacks an adequate interpretation.

Two hundred and seventeen HI profiles at positions approximately 1 ° apart in the bridge region between the Small and Large Magellanic Clouds have been observed with a 15’ arc beam. Diagrams of all the profiles, lists of column densities and average radial velocities are given, together with details of the extensive Gaussian analysis needed to account for the components.

It is shown that the bridge region is most complex. (a) Two radial velocity groups, +214 and +238 km s-1, represent the actual HI bridge between the two galaxies, (b) Three other components, at mean radial velocities of +155, +177 and +195 km s-1 are seen to be integral parts of the SMC, stretching east to R. A. ~ 04h. (c) A further three components in groups at mean radial velocities +253, +272 and +293 km s-1 appear to be extensions of HI from the main body of the LMC.

Nine sets of five closely spaced observations in the lower Magellanic Stream and in the bridge region at high sensitivity supply further information about the region.

In an attempt to determine whether the lithium Une at 6707 Å cornes mainly from the quiet photosphere or from the cooler spots on spotted active stars we have measured Une équivalent widths due to Li and also due to Cal at 6717 Å at various rotation phases on three fast rotating stars, AB Doradus, PZ Telescopium and V 1005 Orionis. The results for AB Dor and PZ Tel show there might be some small rotational modulation which can be linked to the best estimate of the spot position from the available photometry. This moduation is less than that expected on the basis of Giampapa’s work on sunspot spectra. The Li and Cal line equivalent widths were found to anticorrelate.

A spectral line survey for interstellar NH3 is being carried out using the 64-m telescopes at Parkes and Tidbinbilla. Both telescopes are equipped with K-band maser receivers yielding system temperatures below 100 K. The preliminary survey is being made with the Parkes antenna (beam = 1.35 arcmin), with follow-up mapping of the more interesting sources at Tidbinbilla (beam = 0.9 arcmin). The selected sources have in general been HII regions from the H2CO surveys made at Parkes. Statistical results from initial observations of the (1, 1), (2, 2), and (3, 3) lines in the preliminary survey are presented.

The Parkes radio telescope was commissioned in 1961, with an anticipated operational life of 15 years. Twentyfive years later the telescope has been refurbished with the aim of extending its life yet another decade or two. A major undertaking has been the complete replacement of the drive and control System. This presentation outlines the main features of the new System and its effect on the observing facilities offered at the observatory.

Very sensitive low-noise amplifiers designed to receive transmissions from spacecraft are not necessarily suitable receivers for radio astronomy. In the former case a good signalto- noise ratio is required so that high data rates can be achieved. In the latter the ratio of signal to noise power may be as low as 10-4 and the stability of receiver gain and that of ail sources of noise during long integration times become of equal importance.

This paper describes a novel solution to the problem, which allowed important astronomy to be performed while the ruby maser receivers belonging to the European Space Agency were installed on the Parkes radio telescope for an extended period of time.

Adult education classes in astronomy have been conducted in Sydney for many years. The University of Sydney has been especially prominent in this field, holding classes in conjunction with the Sydney WEA prior to 1983, and independently since then. In the last 11 years, most of these courses have been conducted by postgraduate students from the Astrophysics and Astronomy departments in the University’s School of Physics. This paper describes these courses and points out some future possibilities in the teaching of astronomy to adult classes.