The Parkes interferometer consists of the 210-ft para-boloidal reflector of the ANRAO, and a 60-ft paraboloidal reflector mounted on rail tracks. These extend from 400 ft to 1400 ft from the 210-ft paraboloid and run both north-south and east-west. The baseline may be continuously varied during observation; receivers operating simultaneously at 468 and 1402 MHz enable the determination of complete visibility functions over the range 200λ to 2000λ.

The Molonglo fan-beam survey is a digitized survey carried out in March and April 1966, using the 1 mile E-W arm of the Molonglo cross operating at 408 MHz. Three 1´.5 fan beams separated by 1´.5 in right ascension were used. The survey covered the region in right ascension from 10h30m to 18h30m and in declination from +18° to —40°. The region common to the 4C survey has been analysed and we have obtained right ascensions for the 4C sources.

A number of strong radio sources have been examined for structure with the 3’.5 beam of the 80 MHz radioheliograph at the CSIRO Solar Observatory, Culgoora Contour maps of brightness distribution are presented here for the galactic source W44, and the extra-galactic sources Fornax A, Pictor A and 3C353; they are compared, where possible, with maps at other frequencies.

A survey of clusters of galaxies from Abell’s catalogue has been carried out using the Mk II 11 cm receiver recently installed at Parkes. For the present preliminary report only sources with flux densities down to about 0.3 f.u. will be considered, although the sensitivity limit of the receiver is about one-sixth of that value.

A survey has been made of 139 bright southern galaxies using the 1´.5 X 4° fan beam of the E-W arm of the Mills cross. These represent a largely complete sample of galaxies down to a limiting total optical magnitude of ~11.0 when corrected for Galactic absorption by 0.35 cosec β and for internal absorption due to the tilt of the emitting galaxy. Of these, 54 were detected down to a limiting radio flux of 0.4 f.u., at which level the probability of a misidentification is 10%. No a priori distinctions were made between the galaxies on the basis of strong radio emission or optical peculiarities.

NGC 5236 is the fourth galaxy beyond the local group to be investigated at Parkes. Most of the observations were made with a single-channel 21 cm line receiver, coupled to the 210 ft dish. The half-power beamwidth is 13´.5. Declination scans were made through the galaxy, and treated by methods already established for NGC 551, NGC 3002 and NGC 31093. The peak antenna temperature is 1.5°K.

It was first pointed out by Hoyle et al. that quasars if they are indeed located at cosmological distances, must be characterized by an extraordinarily large radiation density : and therefore, though their optical and near infra-red spectra appear to be dominated by synchrotron radiation, any ultrarelativistic electron present must necessarily lose essentially all its energy by inverse Compton scattering. This would mean that, though quasars are emitting fantastic amounts of energy at optical frequencies, they must also be emitting many orders of magnitude more at X-ray and γ-ray frequencies. This paradox has been evaded by several specially constructed models (e.g. Rees and Sciama, Woltjer and Jukes); but the problem has not been removed in general.

A photon with frequency in the range v to v + dv travelling in a direction n̂ within the solid angle dΩ is written (v, n̂).

Considering a mass of gas which is stationary relative to an observer and whose atoms are in continuous random thermal motion, then a redistribution function

The classical theorems on the intensity of radiation (e.g. Milne) depend on the geometry of rectilinear ray trajectories in uniform media. In particular, the theorem concerning the specific intensity I in a medium specified by an isotropic refractive index μ—that, where there are no gains due to emission or losses due to absorption or scattering, the quantity I/μ2 = constant—is proved by assuming that the medium consists of a series of regions of constant refractive index at whose plane interfaces the coefficients of reflection are zero. For these the geometry of the trajectories (Figure 1) is such that, by Snell’s law,

This paper presents results from a series of rocket flights which have yielded the first unambiguous evidence for the variability of a cosmic X-ray source. The evidence rests primarily on three flights, the first two of which were conducted from Woomera by a joint Universities of Adelaide and Tasmania (UAT) team, and the third from Hawaii by the Lawrence Radiation Laboratories (LRL) of California. Data from two additional flights, one by LRL and the other by the University of Leicester, support this evidence.

Recent observations of the Centaurus region by Harries et al., Chodil et al., and Cooke et al. have firmly established the existence of a variable X-ray source, Centaurus XR-2. This source is unique in that its variability has been established beyond doubt.

An albedo X-ray flux from the Earth was observed by experiments which were flown on Skylark rockets during April 1967. The details of the flights and the equipment have been covered in a previous paper. The celestial X-rays observed from discrete sources are superimposed on a diffuse X-ray flux. Most measurements of this diffuse flux have taken the difference between the number of X-rays observed from an area of sky, which is thought to be free of sources, and the flux from the direction of the Earth. By assuming that there are no X-rays from the direction of the Earth, this method removes the high-energy charged-particle background which should be the same in both cases.

We have extended our recent measurements on the extraterrestrial cosmic ray electron spectrum, this spectrum now being determined over the energy range from ~15 MeV to 6 GeV. The extraterrestrial electron intensity between 15 MeV and 200 MeV can be determined unambiguously by studying the diurnal variation of these particles. We have also measured the effects of the 11-year solar modulation on the electrons, thus enabling the electron spectrum observed near the Earth to be extrapolated to the local region of the spiral arm. It is the purpose of this paper to relate these measurements to:

• (i) calculations of ‘secondary’ electrons produced by cosmic ray nuclei moving in the Galaxy; and

• (ii) the observations of non-thermal radio emission from disk components of the Galaxy.

Using a network of ground-based stations stretching from Lae, New Guinea, to the Antarctic, and high altitude balloons and rockets, the Hobart cosmic ray group is studying several aspects of naturally-occurring high energy radiation.

The cosmic ray flux in the energy range 100 MeV/nucleon ≤ E ≤ 1 GeV/nucleon is remarkable for its high degree of isotropy. Observed deviations from isotropy seldom exceed a few per cent and are commonly much smaller. The mechanism responsible for this isotropy is presumed to be multiple, large-angle scattering of the charged cosmic ray particles by irregularities of the interplanetary magnetic field. While generally precluding any hope of discovering a source-related anisotropy of the flux in this energy range, it is just this strong interaction of the cosmic rays with the interplanetary medium that allows the study of the small observed anisotropies, both persistent and transient, to yield considerable information about the structure of the interplanetary medium (the solar wind and its entrapped magnetic field).

A modern coudé spectrograph for observing the spectra of stars and planets with maximum efficiency is a complex and versatile instrument, which represents an investment about equal to that for a 40-inch telescope. The trend toward special telescopes for special kinds of work began in the 1930s with Schmidt telescopes for wide angle photography, and has been followed by the use of specialized telescopes for photoelectric photometry, and more recently by telescopes for polarization measurements. Two telescopes designed for exclusive use with coudé spectrographs already exist—the 48-inch at Victoria and the 60-inch at Haute Provence. More are needed, particularly in the southern hemisphere.