It is generally assumed from an inspection of prints of non-magellanic spiral galaxies that all constituents, including the HI, are distributed with a large-scale circular symmetry in the plane of the galaxy. This assumption is supported by the expectation that any primordial asymmetry in the mass distribution would have disintegrated by the present epoch under the shearing effects of differential rotation into an approximately circularly symmetric ring. It is therefore surprising to find that the recent high-resolution studies of M 31, M 101, NGC 300 and our own galaxy all show that the HI centroid is significantly displaced from the nucleus. This is a sign that the HI distribution is markedly asymmetric.

A large part of the energy lost from interiors of evolving stars at temperatures greater than about 5 × 108°K is carried away by neutrinos. Three neutrino-producing reactions which have been incorporated in various evolutionary models are the photoneutrino process:

direct annihilation of electron-positron pairs:

and the plasma process:

In July 1967 and June 1968 observations of the central intensity variation in several chromospheric lines were obtained by P. R. Wilson and myself at Sacramento Peak Observatory, New Mexico using the 16-inch coronagraph coupled with the high-dispersion Littrow Spectrograph. Observations in the MgB lines (λ5184, 5173, 5167 Å) were obtained the first summer whilst the NaD lines (λ5889, 5896 Å) were studied in the second. Table I shows the mean heights in the solar atmosphere at which it is thought these lines are formed.

Simultaneous high dispersion photoelectric and photographic spectra have been obtained for the short period variables δ Set, δ Del and p Pup over at least one cycle of variation.

The realization that the nuclei of planetary nebulae are stars which evolve with a time-scale of ~ 104 yr (O’Dell,Seaton) has prompted several theoretical investigations of the late stages of stellar evolution (Vila, Divine, L’Ecuyer). Vila has assumed that all nuclear burnings have ceased in these stars, and that the energy release is entirely gravitational. He showed that the inclusion of neutrino energy-loss processes based on the universal Fermi interaction of Feynman and Gell-Mann reduced the theoretical evolution time by two orders of magnitude to a value comparable with the observed time. His theoretical models, however, have effective temperatures greater than those observed by a factor of six.

A study has been made of the upper main-sequence stars in several young clusters, in an attempt to determine a well-defined effective temperature scale for the B stars, and to compare the observed atmospheric parameters with the recent theoretical evolutionary tracks in the H-R diagram (Iben, 1965, Hofmeister et al, 1964, Kippenhahn et al., 1965). Each of the clusters studied contains at least one peculiar A star of the Si λ-4200 type, and this afforded an excellent opportunity for a study of the evolution of these stars.

Pulsar observations will be made with two new general-purpose transit radiotelescopes at present being built near Hobart.

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.

Parker realized that the solar corona would expand into a supersonic wind, whose flow could be described by hydrodynamics. Subsequently a number of such steady state models have been developed which include the energy transport equation. These models assume that the heating of the gas is confined to a thin shell at the base of the corona, but neglect the effects of solar rotation and the general magnetic field, which is carried into space by the solar wind.

During the last solar cycle a number of observations of solar radio emissions were made in a wide frequency range from which an enormous amount of information has been obtained. However the results obtained so far are limited by rather poor angular resolution. Observations with much higher resolution (of the order of 1′ arc) have been required for further studies of solar radio emissions. At the present stage such observations have proceeded in the microwave range; also the radioheliograph at 80 MHz has just started at the Culgoora Observatory. At the Tokyo Astronomical Observatory a high-resolution study of radio bursts in the metre-wave range has been planned since 1960, and the construction of a new compound interferometer operating at 160.3 MHz was started in April 1967 at a new site, Nobeyama. This site, located about 150 km north-west of Tokyo, is surrounded by mountains and quite free from man-made interference. We shall give a brief description of this equipment; details will be published later.

The ionosphere does not behave like a smooth mirror for radio waves, but more like an irregular diffracting screen. When a radio wave is reflected from it, a random diffraction pattern is formed over the ground. Simple arguments can be used to show that this pattern will move over the ground with a velocity which is twice the horizontal velocity of the ionosphere. This phenomenon can be used for the detection of movements taking place in the ionosphere.

There exists a large number of varying methods of solution in radiative transfer theory. House and Avery have recendy published an exposition of the Monte-Carlo technique and the very nature of this solution makes it readily amenable, in theory, to the study of any transfer problem. Grant and Hunt have developed a method involving the invariant Sn matrix transformation and this also appears quite general in its application. Further, the Riccati transformation technique, developed by Rybicki and Hummer, has already been used in solving several different transfer problems. However, these methods have certain disadvantages. The equations are of first order and thus stability difficulties arise. Also, the finer details of the method rely, to a large extent, on the particular problem under consideration, and experience with such a method is required for the efficient computation of solutions.

It can be shown that cepheids pulsating in the first harmonic when evolving through the instability zone at constant bolometric luminosity and mass, are at a given period 0.09 magnitudes bluer than stars pulsating in the fundamental mode. Bell and Rodgers have shown that effective temperatures of cepheids can be obtained by comparison of observed and computed profiles of the wings of the Hα line. Hα cores of cepheids are affected by strongly doppler broadened chromospheric emission and absorption. Using a modified Oke effective temperature-intrinsic colour relation, observations of the Hα line of the Eggen C cepheids β Dor and S Mus have been made at Mt. Stromlo and intrinsic colours obtained for these stars.

In Table I are given photometric data and spectral classes for some OB stars in galactic longitudes 298°-306°. The data have been obtained using a photoelectric photometer on the Reynolds reflector and the Meinel spectrograph on the 100 cm reflector at Siding Spring. Numbers refer to an OB star catalogue in preparation.

Recent astronomical measurements of solar and celestial X-radiation have led to renewed interest in strong shock-wave phenomena arising from explosions which occur on an astrophysical scale as in solar flares, novae and in supernovae. Although on a much smaller scale, the ‘Starfish’ nuclear explosion at an altitude of 400 km over Johnson Island in 1962, provides a useful test of current understanding in this field.

Following the detection of a high flux density from Saturn at 21.2 cm by Davies and Williams and the confirmation by Kellermann, it has been known that the radio emission from Saturn is enhanced at long wavelengths. The Molonglo cross telescope has searched for this emission at 73.5 cm on two occasions, the first in 1967 November when the planet was stationary, and the second during the opposition of 1968 October. Between these dates, installation of preamplifiers on the EW arm doubled the sensitivity of the cross so that although the same procedures were used on both occasions, this paper is based almost entirely on the recent results.

From 1951 to December 1964 the Radiophysics Division of CSIRO regularly operated a solar radiospectrograph at Dapto, N.S.W. This instrument finally spanned the frequency range from 5-2000 MHz with 8 separate receivers, 6 of which used mechanical tuning. Simple rhombic aerials were used on all bands except the 200-2000 MHz band which used a parabolic reflector. The quiet sun could be detected on the latter band only.

During 1965 a section of this spectrograph covering the frequency bands from 10-210 MHz was moved to the CSIRO Solar Observatory, Culgoora, N.S.W., and operated as an interim measure to maintain continuity of observations during the installation of the 80 MHz radioheliograph.

The aim of this work is to investigate certain assumptions that have been made in calculating line profiles and equivalent widths of neutral helium lines in early type stars. The effect of electron scattering on the continuum flux is investigated and a curve of growth analysis carried out to study this effect. The theories involved in calculating the line absorption coefficient are also investigated.

It is evident that the limited duration of a single rocket or balloon flight is a severe handicap to the study of variable X-ray sources like Cen XR-2, the early history of which can only be conjectured from the few available rocket observations. The whole question of the variability of X-ray sources remains in doubt because of the difficulty of relating infrequent high-altitude flux measurements of short duration made with a variety of instruments. There are obvious advantages in a method of monitoring celestial X-ray fluxes from the ground for prolonged periods of time. Such a method has recently been found and, although presently restricted to strong sources like Sco XR-1 and Cen XR-2, is capable of considerable refinement.

An attempt is made to deduce the form taken by the distribution law for radiative scattering events performed by an atom whose energy—level structure is perturbed under conditions appropriate to the quasi-static limit.