Pulse arrival time measurements allow the determination of accurate pulsar periods, period derivatives and, provided the data span is at least one year, precise pulsar positions. If observations are frequent and reasonably regular, irregularities in the period can also be investigated. To minimize the effect of possible variations in dispersion measure, it is important that these observations be made at a relatively high frequency, preferably above 1 GHz. To eliminate pulse shape variations due to variable ionospheric Faradayrotation, the pulse total intensity or one of the circular polarizations must be recorded.

Recent accurate measurements at 408 MHz and 2700 MHz of the positions of 4C catalogue sources have allowed a comparison of the positions of radio sources measured at the two frequencies and an investigation of the frequency dependence of these positions.

A 4-m telescope for mm-wave observations, particularly of spectral lines, was erected in mid-1976 at Epping by Krupp Ltd., Rheinhausen. A cooled mixer receiver was installed on the telescope in April 1977 and a series of test observations made during the remainder of the year, subject to the availability of the receiver and the multi-channel filter bank which were shared with the Parkes 64-m telescope.

Soft X-ray photographs of the Sun taken from the manned Skylab satellite (Vaiana et al. 1973) gave, not the earliest, but perhaps the most graphic evidence that the solar corona is patchy. During the Skylab mission (May 1973 to February 1974), the solar corona as usually envisaged covered only 80% of the Sun (Bohlin 1977). The areas lacking a ‘dense’ corona are called coronal holes (Withbroe al. 1971; Waldmeier 1975).

Oscillatory convective motions have been observed in the umbrae of sunspots and, in the past, the linear theory of overstability has been used for sunspot models. Here a non-linear model for oscillatory convection has been used to investigate the possibility of a preferred horizontal cell size for these motions, in the presence of a magnetic field.

The integration forward in time, from the conductive state, of the non-linear multimode equations governing magnetoconvection when the magnetic Prandtl number is less than one portrays a complex interaction between the evolving magnetic and vertical velocity horizontal scales. Preferred horizontal scales for the convective cells have been established by identifying the modes that substantially contribute to the overall convective heat transport. All other modes, although initially perturbed, in time essentially decay to zero through self interaction.

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).

The Lands Department Building in Sydney is situated on the block bounded by Bridge Street, Gresham Street, Bent Street and Loftus Street. The northern (Bridge Street) end is surmounted by a small copper dome.

Evolutionary calculations have been made for a star of initial mass 17.5 M⊙ in order to emulate the evolution of the precursor of SN1987A. The results give good agreement (i) with the observed properties of Sanduleak -69°202 (star 1) when the model reaches the supernova epoch, and (ii) with the observed distribution of red and blue supergiants in the LMC. Mass loss throughout the life of the star at rates reasonably consistent with observed values is required to produce these results. At the time of explosion, the supernova has a mass of only ∼ 5.4 M⊙ and it is surrounded by about 8 M⊙ of wind material in a shell of ∼0.4 pc radius.

The basic observational evidence for helium-burning red giants in open clusters has been given elsewhere, and I shall give here only a summary and then describe in more detail new results for one cluster, NGC 2477.

The effect of impulsively turning off the dissipation in an existing model for energy propagation through Alfvénic fronts into the coronal site of energy release in a solar flare is examined. In the optimum case of impedance matching, the flux tube re-stresses on a much longer timescale than it relaxes, suggesting an explanation for the timescales observed in homologous flares.

We have mapped the southern galaxies NGC 613, 1313, 1433, 1566, 1672 and 2442 in the 12CO(J = 1 → 0) transition with the 15-m Swedish European Submillimetre Telescope (SEST). The sample is based on galaxies previously observed in radio continuum with the Molonglo Observatory Synthesis Telescope (MOST). Strong emission is seen from the barred galaxies NGC 613 and NGC 2442 and from the active galaxies NGC 1566 and 1672. The weakest emission was from NGC 1433, while the Sd spiral NGC 1313 was not detected.

The object of this paper is to show that librations of the Earth follow conditions that are prescribed by nutations. The poles of rotation, excitation and inertia are treated as moving within a system that has approximately constant speed and direction relative to the Conventional International Origin. Applied excitations are presumed to cause other excitations, part forming at once and part forming progressively.