A Type II solar radio burst is a relatively narrow-bandwidth metre-wavelength emission which drifts outward in the solar corona at a velocity between 500 and 1500 km s-1. It was first described by Wild and McCready (1950) and since then it has been the subject of numerous investigations (see e.g. McLean 1974; Nelson and Robinson 1975).

In recent years, a number of numerical experiments have simulated various aspects of the early stages of star formation (see Tscharnuter 1980 for a discussion and review). In all but one of these experiments, however, the effects of the interstellar magnetic field have been neglected, although observations (for example, see Verschuur 1969) suggest that in some interstellar clouds, the magnetic energy is comparable to, or even greater than, the gravitational and thermal energies. It is also believed (Mouschovias 1981), that at least at the early, diffuse stages of collapse, where the ionizing radiation can penetrate deep into the cloud, the bulk of the neutral matter will feel the magnetic forces via collisional coupling with the ionized matter. Thus there exist no observational, nor theoretical reasons justifying the neglect of the interstellar magnetic field in these numerical simulations.

The Class I/Class II division of extragalactic radio sources by Fanaroff-Riley is a manifestation of important physical differences existing in radio sources.

It is proposed that the division essentially arises from the differing Mach numbers in Class I and Class II jets. The low Mach number, Class I jets are susceptible to turbulence, are decelerated by entrainment of the surrounding medium and maintain an anomalously high surface brightness as a result. The high Mach number, Class II jets are less turbulent and remain supersonic, produce high pressure shocks along their lengths and terminate via a strong shock against the IGM.

An analysis of the energy balance in both types of source reveals jet velocities of the order of 5-10,000 km s-1 for Class I jets and mildly relativistic velocities for Class II jets.

The important rôle of optical and X-ray observations in determining the gravitational field of pressure distribution in radio galaxies will be discussed with examples given of NGC1399 and IC4296.

The globular clusters 47 Tuc (NGC 104) and NGC 6723 both belong to the group of clusters which have late-type integrated spectra and which appear to be only slightly metal deficient with respect to the stars in the Hyades.

The Stellar Interferometer at Narrabri Observatory consists of two large reflectors which focus the light from a star on to two photoelectric detectors. The output currents from these detectors contain fluctuations which correspond to fluctuations in the starlight itself. The fluctuations from the two detectors are amplified in the frequency range 10-100 Mc/s and their correlation is measured by a linear multiplier. This correlation is measured as a function of the separation between the two detectors. It can be shown theoretically that the correlation at any given baseline is proportional to the square of the fringe visibility which would be observed by a classical Michelson interferometer. It is therefore possible from observations of the correlation at different baselines to find the angular diameter of a star.

Supernovae of type II (SN II) are found to exhibit a correlation (r = 0.45 ± 0.15) between M(max) and parent galaxy luminosity. This correlation might be understood by assuming that the metal-rich red supergiant progenitors of SN II in luminous galaxies have more extended photospheres than do those of the more metal-deficient evolved progenitors of SN II on low-luminosity galaxies. For h = 0.5 it is found that SN 1987A was ∼1.5 mag fainter at maximum in blue light than any other well-observed SN II. For h = 1.0 SN 1948B, SN 1973R, SN 1972Q and SN 1987A exhibit comparable MB(max). It would be important to undertake systematic searches for sub-luminous SN II in dwarf galaxies and in the metal-poor extreme outer regions of giant- and supergiant spirals.

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.

In this paper we report an independent determination of the Location of the break (change in spectral index) in the spectrum of the diffuse X-ray background by applying a simple analysis technique to data already in the literature.

Characteristic frequencies of some modes of radial pulsations and their relative displacements have been determined for a sequence of composite polytropic stellar models having an inner zone of index n = 1 and an envelope n = 5. It is demonstrated that vibrational stability increases with the degree of central condensation of the individual two zone models.

The first version of this mission was approved by the European Space Agency (ESA) Council in 1973 but did not infact start its Phase B study until 1977. The early baseline design had been constrained by the requirement to make the spacecraft compatible in size and weight with the performance of a NASA Delta rocket, since this was seen as a necessary back-up to Ariane, then at an early stage of development. The mission payload then evolved with time due to the changing role dictated by the technical successes and observations made by the series of well-known X-ray satellites. The final spacecraft has emerged to have a unique capability since all the other X-ray satellites except the small Hakucho have now expired.

Astonomy in Sydney predates Sydney Observatory by some 70 years. Lt William Dawes arrived with the First Fleet and set up an observatory at a place now called Dawes Point at the foot of the present Observatory Hill. His instructions were to observe a comet predicted by the famous astronomer, Edmund Halley, to return about 1790.

The initial flight of the University of Tasmania balloon-borne X-ray telescope was made from Parkes on Dec. 2, 1976. During the flight, enhanced X-ray emission was observed from the directions of 3U0900-40 (Vela XR-1), GX301-2 and the Galactic Centre. In this paper we report on the performance of the payload during the 11 hour flight and describe the preliminary results thus far obtained.

A low-cost differential image motion monitor (DIMM), consisting of an 11-inch Celestron, an SBIG ST-4 autoguiding CCD camera and a PC, is described. Two such systems were used during June–July and November–December 1993 to make near-simultaneous seeing measurements at Freeling Heights in the Northern Flinders Ranges and at Siding Spring Observatory. The results of these campaigns show that the seeing-distribution is generally similar at both sites, with the most common seeing value being ~l·2″. Siding Spring does, however, have slightly more bad seeing (>2″) than Freeling Heights. Weather records from Arkaroola Resort (15 km south of Freeling Heights) indicate that there is ~15% less cloud cover at Freeling Heights than at Siding Spring. Episodes of rapid seeing deterioration at Siding Spring in winter are shown to coincide with warm air masses crossing the mountain.

The small group of known Seyfert galaxies (Seyfert 1943) is of interest because it is clear that some violent activity is occurring in the nucleus, and some of the properties suggest a relationship with quasi-stellar sources. The spectrum of a Seyfert galaxy consists of strong, often very broad, emission lines superposed on a continuous spectrum which in some cases shows no absorption-line features. Two of the galaxies, NGC 1068 and 1275, are radio galaxies and the latter is known to be variable at radio frequencies (Dent 1966).

Cosmic rays produce a component of photomultiplier noise which often dominates the high amplitude region of the noise pulse height spectrum and which is not reduced by cooling the tube. The source of the noise is Cerenkov radiation produced by individual high energy cosmic rays in their passage through the glass envelope of the tube, principally in the glass faceplate on which the photocathode is deposited.