The discovery of pulsars in 1967 marked the watershed of interest in short-time-scale phenomena in radio astronomy. Ionospheric scintillation on time scales of seconds, interplanetary scintillations at tenths of seconds and solar bursts of similar duration had already been studied. But with pulsars individual pulses contained subpulses of width about 10 ms, and later observations of microstructure were to show that structure with scales of 10—100 μs were present. In other areas searches for the 10—100 ms radio pulses expected to accompany the gravitational wave events resulting from stellar collapses were made, and more recently searches have been made for the radio pulse accompanying the explosion of small black holes (Rees 1977). Work in this area is summarized by O’Sullivan et al. (1978) and Phinney and Taylor (1979).

A small astronomical observatory has been constructed on the edge of the Macquarie University campus at North Ryde in Sydney. It will be used primarily for photoelectric observations of variable stars. Further improvements to the present observing system are being planned and observations have already started on β Cepheids.

Ammonia was searched in the direction of 46 sources placed in the southern hemisphere where H2CO or H2O was detected previously. Observations were carried out at Itapetinga Radio Observatory, Atibaia, Brazil using a 13.7 m paraboloid. The receiver used for these observations had a K-band ruby travelling wave maser as a preamplifier and the system temperature ranged from 250 to 300K. All sources were observed at least twice, each observation lasting for 30 minutes. The filter bank used consisted of 47 contiguous channels with 100 kHz bandwidth. Results are presented on Table 1 — Positive results and Table 2 — Negative results.

This work is aimed at understanding the phenomena which affect the sharpness and stability of optical images transmitted through the atmosphere. A brief description is given of the results obtained to date from an experimental field-study directed at establishing a connection between optics and meteorology. Most of the work has, so far, been conducted in daytime because our main application is to solar astronomy; other fields such as surveying, aerial reconnaissance and so on can also benefit from basic research in atmospheric optics.

A horizontal line of sight over uniform, level terrain presents the simplest case for study. The optical transfer function (OTF) of the system comprising an air-path and telescope objective has been measured with an image analyser which is a modified form of stellar seeing-monitor. The outputs of this analyser are proportional to the modulus and argument of the OTF. The modulus, or modulation transfer function (MTF), is a measure of image contrast; the fluctuations of the argument measure image movement, or “dancing”. The OTF is a function of spatial frequency f (cycles per unit distance) which may be altered by radial movement of the scanning graticule of the image-analvser.

Photoelectric B and V light curves and high dispersion spectroscopic observations were obtained in 1985 February for the rapidly rotating spotted star HD 36705. The visual light range was about 0.09 magnitude, with a well correlated B-V change of approximately 0.04 magnitude, the star being redder when faintest. There is evidence for a broadband flare of ~0.05 magnitude in V and 0.07 magnitude in B. This occurred near maximum light.

Spectroscopic observations show a variation in the equivalent width of the Ca K emission by a factor of about two in antiphase with the photometric variations, maximum emission corresponding to minimum brightness. This is probably due to bright plages and enhanced chromospheric heating associated with the photospheric starspots.

High dispersion, high signal-to-noise spectroscopic observations confirm the presence of lithium λ 6708 as reported by Rucinski (1982, 1985).

Several interpretations of the nature of HD 36705 are discussed; however at present none is completely satisfactory and further observations are required. As the star is probably at less than 100 pc, a parallax determination may be possible, and could help answer many of the questions concerning HD 36705.

Since the discovery of variable circular and linear polarisation in VV Puppis (Tapia 1977), several investigators have observed the system. The new observations particularly of polarisation (Liebert et al. 1978, Liebert and Stockman 1979 have ruled out the standard dwarf nova (accretion disc — hot spot) model previously used to interpret the light curve of VV Puppis.

Balloon borne alt-azimuth mounted X-ray telescopes flown from Hyderabad, India (17°N), Palestine, Texas (32°N), and Mildura, Australia (34°S), have detected hard X-rays (hv>20KeV) from discrete sources in the Cygnus region.

In the past a number of analytical solutions have been found to the differential equation for small radial adiabatic oscillations of stars, with the aid of a series expansion of the form leading to a two-term recurrence relation.

The advent of new techniques to measure the global oscillation spectrum of the Sun has provided a new and powerful tool to investigate solar structure. One of the most challenging and potentially rewarding problems in contemporary astronomy is to devise techniques which will allow similar studies of other stars. This paper outlines the theory of global oscillations of late-type main-sequence stars, and summarises some of the achievements of global oscillation studies of the Sun. It then reviews the very few successful attempts that have been made to study stellar oscillations, and briefly discusses several apparently promising lines for further instrumental development.

It is well known that the wings of the solar sodium D-lines cannot be predicted successfully using present line-broadening theories and elemental abundances derived from an equivalent-width analysis of the weak lines. By far the most important cause of broadening of the D-lines is collision broadening by neutral hydrogen.

In this paper we summarize the results of radio studies of the distribution functions (number, energy distribution and pitch angle distribution) of the energetic particles that are produced at the time of solar flares. We consider the clues and constraints they impose on the mechanisms of acceleration, bearing in mind that radio evidence implies that there are at least two stages of acceleration in many flares.

In the following sections we discuss the distribution functions of the particles resulting from (a) first phase acceleration, (b) first and/or second phase and (c) second phase acceleration. Table I summarizes the results.

Radio position measurements with an error of <2” arc rms allow reliable optical identifications of compact radio sources to be made solely on the basis of radio-optical position coincidence. In this way neutral or red stellar objects, faint compact galaxies and faint QSOs can be reliably identified. Such identifications are of particular interest because they are rich in BL Lac objects, high-redshift QSOs, QSOs with unusual optical emission or absorption spectra and galaxies with active nuclei (see Jauncey et al. 1978).

Most of the recent advances in X-ray astronomy have resulted from satellite observations in the low energy (< 20 keV) range. The Einstein X-ray Observatory in particular has been responsible for a dramatic increase in our knowledge of the X-ray sky, in that all major classes of astronomical objects have been detected.

The conventional method of measuring the radiation diagram of an antenna is to rotate it in the field produced by a fixed point source located in its Fraunhofer zone (Hollis et al. (1970)). With the very large antennas typically used in radio astronomy this presents difficulties. For example, to measure the 64 m telescope at ANRAO, Parkes at frequencies in the OH transition lines band (1.6-1.7 GHz), the source, to be located in the Fraunhofer zone, must be located at least 50 km away and then at a sufficiently high angle to allow measurements free from ground effects to be made. Clearly there are no terrestrial means to accomplish this.

The cosmic ray ground-level enhancement (GLE) of 24 October 1989 was the last of a series of GLEs associated with the same solar active region. Intensity enhancements were observed by at least 31 neutron monitors in the worldwide network, with the largest increase (~200%) observed at South Pole, Antarctica around 20:30 UT. Using a least-squares model fit to all available neutron monitor data, spectra, apparent source directions and particle pitch angle distributions have been derived. The effect of disturbed geomagnetic conditions has also been taken into account.

A new method for solving heat diffusion in three dimensional particle simulations is described. The difficulties encounted by other authors is discussed, in particular the difficulty of including boundary conditions in particle simulations. One and three dimensional tests of the method are described.

This paper discusses the observation of molecular hydrogen line emission outside near-infrared wavelengths, and in particular the opportunities afforded to molecular astrophysics by studies in the mid- and far-infrared.

Absorption limits the distances at which X-ray sources may be observed at low photon energies (≲3 keV). Several authors have estimated the X-ray absorption coefficients of the interstellar medium by assuming a chemical composition such as that given by Aller for the general abundances of the elements.

In calculating models of stellar interiors convection is almost always treated by assuming that it is present if and only if the Schwarzschild criterion is satisfied. It seems possible that this oversimplifies the actual situation. In particular convective motions may overshoot beyond the formal boundary of the convective core, as given by the Schwarzschild criterion. The principal result of such overshooting would be the mixing of additional material into the core. This sort of additional mixing has been considered by Maeder (1974) and by Prather and Demarque (1974) in relation to the evolution of stars away from the main sequence in old open clusters.