The internal constitutions of the terrestrial planets Mars, Venus and Mercury are investigated through the use of ‘equations of state’ empirically derived for particular internal zones of the Earth. The equations usually take the form of tabular relations between the pressure p and density p, temperature dependence being treated as of secondary consequence. In using p rather the full stress tensor in solid zones, i.e. in using a hydrostatic theory, the effects of strength and deviatoric stress are also treated as of secondary consequence. Except for the use of data on the ellipticity ∊ of figure of a planet to provide evidence on the moment of inertia I, the planets are treated as spherically symmetrical.

One of the interesting questions in solar X-ray astronomy is the question as to whether the hard X-ray emission which occurs during major solar flares is a thermal or nonthermal phenomenon. The evidence for non-thermal emission has been based in large measure on a balloon-borne experiment by Peterson and Winckler, which constituted the first detection of high energy flare X-rays. In the Peterson-Winckler experiment, the incident solar X-rays were measured by both an ion chamber and a Geiger counter photometer, and from the ratio of responses, the hardness character of the incident X-rays was reduced. It was concluded that the observed result could have been explained in terms of the sudden non-thermal production of a group of electrons with energy of the order of 500 kilovolts.

It is usual to describe the motion of the planets around the sun in terms only of the gravitational forces between them. The purpose of this note is to point out that another form of interaction between bodies in the solar system is possible through the medium of the solar wind.

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).

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.

Over the past years considerable information has been acquired concerning the structure and magnitude of sunspot magnetic fields; however, there is a paucity of data concerning the motions of the seats of these fields, i.e., individual umbrae within a spot group. The well-known effects of differential rotation cause sunspots to diverge with time in longitude at a daily rate of, at most, a few degrees per solar rotation. On the other hand, a limited number of investigations have shown that individual umbrae can have proper motions of up to 100 to 200 m/s, or about ten times greater than effects of differential rotation. In addition, equally limited observations have shown that umbrae sometimes rotate about an axis through their centre; in an extreme case the rotation reached 30°/day. The last large sunspot group of the last cycle, having Central Meridian Passage 20.5 September, 1963, has been studied by means of photoheliograms and magnetograms obtained four days before and four days after CMP at the Crimean Astrophysical Observatory. The magnetograms show the distribution of both the transverse and longitudinal components of the magnetic field in the activity region. In this study we have studied umbral motions and their relation to the magnetic field.

I am reporting here work done recently by the astrophysics group at the University of Queensland (notably G. D. Finn and R. L. Young). We are interested in the detailed formation of the profiles of the sodium-D solar absorption lines. These lines are very strong with extended wings and the object of the exercise is to determine how closely, under the physical conditions assumed to exist in the solar atmosphere, we can theoretically reproduce the detailed line profile which is observed.

It has become recognized that the dominant mechanism in the formation of the cores of resonance lines in the solar spectrum is non-coherent scattering, e.g., Thomas (1957). A study, preliminary to the theoretical investigation of the spectra of chromospheric structures, is the evaluation of the effect of diffuse reflection and transmission by non-coherently scattering media.

We have used rocket-borne photometers to determine the ultra-violet flux of the full moon in the wavelength range 2400-2900A where atmospheric ozone prevents ground-based observations. The lunar fluxes determined in two rocket firings from Woomera on 9th December, 1965, and 30th August, 1966, are summarized in the Table. The results for the two firings have been corrected to full moon values on the assumption that the lunar phase law is the same at these ultra-violet wavelengths as it is in the visible.

Dodson and Hedeman discovered an unexpected effect in the occurrence of solar proton events as revealed by polarcap absorption (PCA). When the 48 events in Bailey’s Catalog of the Principal PCA Events, 1952-1963 are distributed with the phase of the moon there is a gap of several days near full moon; also, many more events occur when the moon waxes than when it wanes. Dodson and Hedeman did not find similar, apparent departures from random distribution either with a mean solar rotation period of 27.3 days or for solar flare events. They concluded that ‘at the present time it is not clear whether the 29.5 day “effect” is related to the sun or the moon or is only a statistical accident’.

The only planet with observed secular motion between the body and the axis of rotation is the Earth itself, which rotates both progressively and with unexplained librations about equatorial axes.

A morphological comparison between radar meteor survey data obtained at Ottawa (Millman and McIntosh, 1964) from 1958 to 1962 and that obtained from Christchurch (Ellyett and Keay, 1963) in 1960-61, confirms that the Daytime Arietid, Delta Aquarid meteor shower association is the most prominent feature of the annual activity. The data from Canada and New Zealand are easily reconciled as far as this activity is concerned and also for the weaker Eta Aquarid shower which, having a radiant at zero declination, is equally prominent in both sets of data. Furthermore, the data from both hemispheres is consistent with a forty per cent increase in overall activity during the second half of the year.

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.

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.

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.

Photographic observations of Flare Stars in association with Slee, Higgins and Patston, T Association patrols, photographic photometry of selected variable stars in association with Bateson of New Zealand and surveillance of comets brighter than V = 13m, in association with Candy of the United Kingdom constitute the principal fields of research of Page Observatory (private), situated 7 miles North of Brisbane. A recently constructed f2.9 8in/12.5in Schmidt telescope now serves as the main photographic instrument.

This cluster has two notable characteristics: it contains more than 80 variables, and relative to its NP half its SF half is covered by a cloud absorbing up to a magnitude in the blue. These properties make it an ideal object for determining the ratio Av/E of V absorption to colour excess—one simply compares mean colours and magnitudes of variables in the obscured part with those in the clear part.

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.

Wildey (1961) and Tifft (1963) have both done photographic photometry in two colours of 47 Tuc. They found a colour-magnitude (c-m) relation which is characterized by a very short red horizontal branch and a giant branch which is redder at a given magnitude and fainter at a given colour than that of any other globular cluster. Eggen (1961) obtained an ultraviolet excess of 0m.19 for 8 cluster members bluer than B-V = 1m.4 and of 0m.21 for 7 stars redder than this, assuming negligible reddening for the cluster.

A preliminary investigation of this cluster was carried out by Gascoigne and Ogston (1963). They found that the cluster is probably a disc type globular on the basis of the c-m diagram down to the horizontal branch and its integrated spectral type (G2).