The Sydney University Stellar Interferometer (SUSI) uses siderostats (plane, alt–azimuth mounted mirrors) to reflect starlight into the instrument. The analysis of the pointing and guidance of the siderostats by traditional methods is not practical and vector algebra has been used to develop the required algorithms. Real siderostats will not be ideal and can be modelled by a set of parameters. The methods for determining the model parameters and for incorporating them into the guidance and pointing algorithms are described. Field rotation also affects the operation of SUSI, and the field rotation angle and related quantities are also determined.

The problem of synchronizing clocks at a distance has been solved both by the use of travelling clocks (e.g. caesium beam devices) and by radio transmission of time signals, for which active satellites are used to overcome inherent errors. A group of Czech workers recently developed a method of intra-continental clock comparison which makes use of the properties of domestic television signals. This has been verified under Australian conditions in experiments carried out between Mount Stromlo Observatory and the Division of Applied Physics of the National Standards Laboratory, CSIRO, Sydney, using signals from the Australian Broadcasting Commission transmitter ABWN 5A Wollongong.

The Tidbinbilla NASA Deep Space Network tracking station near Canberra employs 64-m and 34-m antennas for deep space vehicle communication. Regular use is made of the facilities for radio astronomy via a host country agreement between the United States and Australia. To support the expanding astronomical use of the station, and in particular for the Tidbinbilla two-element interferometer (Batty et al. 1977), a small computer was installed early in 1980 to control observations. The system will also be used for as much data analysis as possible to minimize off-site computing.

It appears that the relative number of β–Cephei variables among the early B stars is comparable to the fraction of the evolutionary lifetime spent in the secondary contraction and early shell-burning phases (Lesh and Aizenman 1973a) and it may therefore be of some interest to investigate possible instability mechanisms associated with hydrogen shell-burning in stars within the mass range of 10 to 15 M ⊙ (Lesh and Aizenman 1973b).

The height-integrated Pedersen and Hall conductivities are calculated for the weakly ionized region of the solar atmosphere in the vicinity of a sunspot. The values obtained are much larger than previous authors have estimated. Dynamo theories for solar flares which rely on the photospheric region having a large resistance are untenable.

A few years ago Fowler (1972) published a paper in which he proposed two ‘desperate explanations’ for the solar neutrino problem. Desperation continues to be characteristic of the subject, for, in spite of many investigations over recent years, there is still no unambiguously successful model satisfying all the observational features of the Sun and giving a predicted neutrino count rate below the Davis (1972) experimental limit.

Continuous, wide sky coverage is essential for the detection and monitoring of infrequent, short-lived events of astrophysical interest such as supernova and nova explosions, variable X-ray sources, gamma ray bursts, gravity waves and stellar and solar flares. We propose to (1) examine past radio propagation records and (2) develop new computer based radio receivers to monitor and log ionospheric perturbations associated with these events.

In recent years, a large amount of work has been directed towards understanding the process of star formation. However, despite these efforts, there still remain areas largely unexplored, where theories are only justified by approximate qualitative arguments rather than fully three dimensional calculations.

On 14 March 1986 the European Space Agency’s Giotto spacecraft passed within 600 km of the nucleus of Halley’s comet. During the encounter a radio science experiment was conducted with the aim of determining the total amount of cometary material which impacted the probe. In this paper the theory and implementation of the experiment are discussed and a summary of experimental results is given.

As has been previously stated (van der Borght) the lengths l 1, l 2, l3 and l 4 are functions of and so a discussion of these lengths is in fact a discussion of the f’s. For a first approach to a determination of these f’s, a standard Vitense2 model of the convection zone—with mixing length l, is used. We assume that l = H. The variables we need are kz , which are the vertical wave number associated with the characteristic eddy, the average vertical velocity, and the average (non-dimensional) temperature fluctuation. These quantities are approximated, using the following relations

The polarisation observations of the central region (containing the jet) of the galaxy M87 were obtained in May 1980, with the polarimeter (Visvanathan 1972) attached to the f/15 cassegrain focus of the AAT. The IPCS was used in direct mode to record the images of the field. Figure 1 shows a single, raw image of M87 in the light of B (the image shown is 90 arcsec square). The knots referred to in the text are marked. One complete observation consists of 12 images of the object field, corresponding to the 12 selected position angles of the polaroid filter, rotated from 0° to 330° in 30° increments. The Taurus software (Taylor and Atherton 1980) was used to increment the data to the relevant memory location. The data were stored on tape after a sufficient number of complete rotations of the polaroid were completed.

Observations of transient solar radio emissions lasting 0.2 to 2 s in the frequency range 25-50 MHz have demonstrated the existence of a characteristic and relatively common type of burst (the split pair) made up of two narrow band components separated in frequency by about 0.1 MHz.

The observations in this paper were carried out as part of a program co-ordinated by the Occultation Section of the Royal Astronomical Society of New Zealand.

On 6 August 1989 minor planet (9) Metis occulted the magnitude 8.7 star SAO 190531. The occultation was observed by two visual observers in Tasmania, and at one photoelectric and two visual sites in New Zealand. From the five chords obtained we have deduced an average cross-sectional diameter for this minor planet of 173.5 km at the time of the occultation. This is in good agreement with previous radiometric and polarimetric results.

Recently I have carried out a two-dimensional radiative-transfer analysis of the data given by Edmonds on centrelimb relative rms intensity fluctuations in terms of horizontal temperature fluctuations in the solar photosphere. Edmonds himself attempted an analysis of his data and found a ΔT rms which increased monotonically from about 300°K at unit mean optical depth (i.e. at a given physical depth) to 500°K at optical depth 3.

A one-day workshop discussed the properties of shocks in star-forming regions. It also reviewed other physical processes in star-forming molecular gas, and the progress in numerical modelling of such physics. Discussion concentrated on the complexity which instabilities in the gas flow bring to the analysis of shocks. The consensus was that progress will be made as the spatial/spectral resolution of shock measurements improves, and as numerical modelling of the nonlinear growth of instabilities becomes possible, potentially leading to statistical models of shock dynamics.

Seeing measured in the open air with a differential image motion monitor (DIMM) is compared with seeing measured simultaneously at the Cassegrain focus of the Anglo-Australian Telescope (AAT). It is shown that when the mirror is hotter than the dome air, the AAT’s seeing is degraded by ~1 arcsec per Celsius degree of excess mirror temperature. The consequence of this is that mirror seeing currently contributes significantly to the seeing at the AAT on many nights. A mirror colder than the dome air does not seem to degrade seeing, and neither does an internal-to-external air temperature difference of up to at least 3°C when the venting fans are on.

The metal content of stars (and galaxies) is of great interest as it relates to the theories of element formation, and through these to the history of our galaxy, the frequency of supernovae, the star formation rate and even the quasar rate. The kinematics and metallicity of stars have been correlated in a theory of formation of the galaxy by Eggen et al. (1962). Alternate theories (Unsold 1969) have also been proposed. Much work has gone into isolating individual metal deficient stars and determining their abundances, and also the abundances for stars in clusters.