Astronomical spectrographs are usually mounted at one of three focal positions on a reflecting telescope: (1) the Newtonian focus, at the top of the telescope tube, with only one reflection from the primary mirror, where the spectrograph must be small and light, and designed for low resolution on faint objects; (2) the Cassegrain focus, behind the cell of the primary mirror, with a total of two reflections, where the spectrograph can be appreciably larger, to give intermediate resolution; and (3) the coude focus, at a fixed location below the end of the polar axis, with three, four or five reflections, where there is no limit to the size of the instrument, and where resolution is limited only by the brightness of the object and the light efficiency of the system. This is the ideal location for image tubes, Fabry-Perot interferometers, and equipment for Fourier spectroscopy.

The function of the 158 MHz interferometer operating at the CSIRO Solar Observatory, Culgoora, N.S.W., is the measurement of solar radio burst positions at a frequency close to the second harmonic frequency of the radioheliograph. The interferometer is designed to measure the north-south and east-west position co-ordinates of an isolated active region on the Sun with an accuracy of ~1′ arc, at rates up to 16 s−1.

The possibility of the occultation by Neptune of a star of similar apparent magnitude to itself was first pointed out by the amateur astronomer Ross A. Shuart. It was clear that such an event would provide data on Neptune’s position which would be of value to the observatories which produce the planetary ephemerides. The existing ephemeris of Neptune is known to contain small errors which have been accumulating over many years.

In a recent paper Aizu and Tabara list 36 radio sources classified as supernova remnants (SNR). Some of these identifications are based on low-resolution radio data and are consequently unreliable. Using the Parkes 210-foot radio telescope at 635, 1410 and 2650 MHz (beamwidth 31′, 15′ and 8′.4 respectively), E. R. Hill and the author observed the seven sources listed in Table I. Of these seven, there is close agreement with Aizu and Tabara’s data only in the last one (3C396.1), and we agree with the SNR classification, with certain reservations, for only three of these sources.

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.

In an early paper Sterne investigated the pulsational properties of three stellar models with specified density distributions. He assumed a solution for the relative amplitude of the displacement to be of the form and on substitution into Eddington’s equation for small radial adiabatic oscillations of a star obtained a two-term recurrence relation to solve for the an in the case of each model.

A redistribution function R(x, x′)dx dx′ is defined as the probability that a photon with frequency between x and x + dx will be absorbed by an elemental atmosphere which then emits another photon the frequency of which lies in the range from x′ to x′ + ax′. The frequencies x and x′ are measured from the central frequency νo of the spectral line in units of the Doppler width Δ The particular functional form taken by R(x, x′) in this discussion will be given by

where α represents the broadening of the spectral line in units of the Doppler width while the function H(o, z) is defined by

the Voigt function. The function defined by means of equation (1) is one of that class of redistribution functions which combines natural and Doppler broadening. Therefore, it should be expected that any results obtained using this particular redistribution function will exhibit certain features characteristic of this type of scattering.

The study of plasma instabilities described by the inclusion of a finite conductivity in the hydromagnetic equations has aroused considerable interest since the initial work of Furth, Killeen and Rosenbluth for a two-dimensional geometry. In particular, the so-called ‘tearing’ mode, which has been observed in laboratory plasmas, has been suggested as a possible source of energy for solar flares.

A recent measurement of muon flux at energies greater than 1012 eV provides evidence for muon production by a process other than pion decay in cosmic-ray showers. Near this characteristic energy, the existing theory of weak interactions requires modification if it is not to violate a limitation (2) imposed by unitarity, which represents the conservation of probability. This work is an examination of modifications that are needed if the framework (4) of the theory is to be retained.

The object of this contribution is to report the galactic background intensity at 2 and 3 MHz. The observation is an extension of earlier work which the noise temperatures at 50, 30, 20, 10 and 5 MHz were obtained at 65°N declination by means of identical antennas of beamwidth 70° between half-power points. As discussed in the earlier work, the temperatures were obtained separately in the ordinary and extraordinary modes, in order to account for the attenuation in the ionosphere.

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.

Photo-electric observations of the occultation of BD —17°4388 by Neptune on 1968 April 7 were made with instruments and techniques as listed in Table I. A preliminary report of these observations has been given in IAU Circular No. 2067.

A powerful approach to the understanding of any group of stars is the study of any companion stars which can be shown to be physically connected. But RR Lyrae variables, in common with other members of Population II are deficient in physical pairs. Baize’s catalogue of variables with companions contains only one: CSV 1795 = ADS 9354 A. As far as can be determined no period or light curve has been published for this star and it remains doubtful whether it is an RR Lyrae variable.

The study of the sources of the slowly varying component at decimetre and centimetre wavelengths has been a major preoccupation of solar radio astronomers. Grating interferometers and other high-resolution aerial systems have enabled the separation of the S-component from the Sun’s total emission, and the study of individual sources. Nevertheless much of value remains to be derived from whole-sun intensity measurements—the most basic solar radio observation.

In designing a stellar spectrograph, it is pointless to exceed the resolving power necessary to obtain all the information from the spectrum of a star. This is limited mainly by atomic thermal motions, giving rise to the Doppler broadening of spectral lines, by turbulence and rotation of the stellar atmospheres in which the lines are formed, and by collisional broadening.

Much of the information regarding the nature of solid particles in interstellar space has been gained through the study of the line-of-sight extinction of starlight and the polarization of starlight by these particles. Study of the optical properties of these particles can be extended through consideration of the scattering of stellar radiation in reflection nebulae. This type of approach requires the adoption of models for the star-nebula system, and the grain type to be considered. These models are then used in a theory which describes the scattering of light by an ensemble of small particles, as applied to dust nebulae. Results are thus obtained for the colour of the nebula as a function of distance from the illuminating star. These results can then be compared with the corresponding results of experimental broad-band photometry.

It is a well established observational result that young stars exhibit differences in chemical composition. The differences are comparatively large. For example, some stars have metal abundances as high as 3/2 solar-value while others have abundances as low as 1/2 solar-value. The result was obtained through spectroscopic and photoelectric studies of stars with ages of a few times 108 yr and indicates that the interstellar medium is chemically heterogeneous at the present epoch.

The accuracy of the absolute value of solar flux depends on the temperature calibration techniques and the knowledge of the gain of the aerial used for the measurements. Recent advances in low-noise receivers, microwave components, and amplifier stability have reduced considerably the errors due to temperature calibration techniques. At present the knowledge of the gain of the aerial used for calibrations (usually a pyramidal horn) presents the largest source of doubt of an absolute calibration. Investigations of this problem suggest that a ‘standard gain horn’ should be employed at all observatories in absolute solar calibrations.