A radio-astronomical observation in its most complete form is a determination of intensity and polarization as functions of frequencyf, time t, and position in the sky. An actual observation is usually much less complete.

This review is concerned mainly with the solar modulation of galactic cosmic rays and the progress that has been made since the Tenth International Conference on Cosmic Rays (Calgary, June 1967), My aim is to set out some of the advances in the basic theories; to indicate why certain disagreements between convection-diffusion theory and observations (noted in Webber’s invited review at Calgary) are to be expected; and to indicate some of the currently emerging areas of interest.

A knowledge of the quantitative chemical composition of the primordial solar system must underlie all comprehensive studies of its origin and evolution. Usually we take the composition of the surface layers (photosphere) of the Sun as representative of this composition (except perhaps for deuterium, Li, B, and Be).

Solar X-ray bursts observed by a proportional counter carried on the IMP-F satellite have been analysed for correlation with optical Hα flares and radio bursts. The solar X-ray flux at energies greater than 3 keV was measured each 82 seconds and consisted of impulsive bursts superimposed on a slowly varying X-ray background. During June and July 1967 there were an average of ~10 bursts per day with intensities greater than 400 photons cm−2 s−1 (2 × 10−6 erg cm−2 s−1) which was the threshold for observation of a burst.

The outburst and storm of more than four hours’ duration that accompanied the importance 2 flare beginning at 0h25m U.T. on 9 June 1968 were observed at 80 MHz with the Culgoora radioheliograph. More than 104 heliograms in both senses of circular polarization were recorded at one-second intervals both as cathode-ray-tube photographs and as digital characters on magnetic tape. It is the purpose of this preliminary account to summarize these observations and bring attention to a new phenomenon observed before the start of the flare.

Detailed observations of the importance 2 flare of 9 June 1968, 00h25m U.T., were made at Culgoora in both its Hα and 80 MHz radio emissions, and the event should provide an opportunity for careful study. In this paper a description is given of the radio spectral observations (25-200 MHz) taken at the same site. These observations were among the first to be taken with a newly constructed spectrograph.

Radio pictures of the Sun from the Culgoora radioheliograph have already shown instances in which flares have initiated radio bursts in parts of the Sun remote from the flare position. In this paper we discuss two such events on 1968 May 4 and May 6, in each of which it appears that shock-waves arising from a flare produced distant prominence activity which led to the generation of metre-wave continuum radiation.

On 17 June 1968 we observed a flare event with the 80 MHz Culgoora radioheliograph consisting of a sequence of two type II bursts followed by enhanced emission possibly of type IV. In this paper we shall attempt to summarize some ofthe profuse data collected by the radioheliograph during this event and relate it to data from the radiospectrograph and Hα films of the associated flare (the Hα films were kindly made available by the Division of Physics, CSIRO).

Since its discovery in 1964, interplanetary scintillation has become recognized as a valuable method for investigating the solar wind and the small-scale structure of the interplanetary medium. A particular advantage of the method lies in the ability to study those regions of the medium outside the plane of the ecliptic. To date little has been written about the relation between interplanetary scintillation and solar activity, although regular observations of the source 3C48 during 1965-6 have indicated that a small correlation may exist between the scintillation index and sunspot number. It also appears that anomalous increases in the scintillation index are, on occasion, related to strong flare activity on the Sun.

A natural introduction to this topic is a brief discussion of two phenomena observable in interplanetary space near Earth—the energetic storm particle event (ESPE), and the recurrent Forbush decrease.

Ground level detectors observed several major changes in the primary cosmic-ray flux during November 4960. Large increases, of solar origin, occurred on November 12 and 15, and a smaller one on November 20. The galactic flux in the region of the Earth was severely reduced by a Forbush decrease on November 12, and remained notably depressed until November 25. Considerable magnetic activity was observed throughout the period. Several models have been proposed to account for these observations.

This paper is a progress report on an examination of the short-term variability of solar proton flux in interplanetary space at times of solar flare activity. The data are from the GRCSW cosmic-ray detector on board the Pioneer 7 space probe, which, at the times to be discussed, was more than a million miles from the Earth.

Since 1957, the University of Tasmania has operated cosmic-ray meson telescopes at an underground site near Hobart for the purpose of monitoring the intensity variations in the high energy component of the primary flux near the Earth. Details relating to the site, equipment, and meteorological influences on the observed intensity have been given previously. At a depth equivalent to 36m of water (36 m.w.e.), the equipment responds to an effective primary spectrum having a mean particle energy in the vicinity of 200 GeV and falling off rapidly at low energies, so that about 90% of the primaries have energy exceeding 50 GeV. The corresponding mean energy of response for surface muon telescopes at Hobart is about 25 GeV, while a neutron monitor at Hobart has a mean response at about 7 GeV.

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.

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.

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.

Primary cosmic rays passing through the solar system carry with them valuable information about solar and astrophysical phenomena in the form of intensity and spectral variations. In order that this information be efficiently extracted from observations of the directional cosmic-ray flux at the surface of the Earth, it is essential to have accurate information available to enable the relating of the observed secondary cosmic-ray directions of motion and intensity to those outside the range of the disturbing terrestrial influences.

The interaction of the solar wind and the Earth’s magnetic field causes the field to be confined within a region shaped like a liquid drop. The solar wind flows past this region, the magnetosphere, without penetrating it. The precise shape of the magnetospheric boundary is of interest for hydromagnetic studies, but these usually begin from assumptions about the nature of the magnetic field. Any specification of the boundary which makes no reference to the field must therefore allow more flexibility in such studies.

The present knowledge of atomic spectra is quite impressive but is far from satisfying all needs in fields such as astronomy. The first and second spectra of many elements have been analysed into energy levels but the spectra of the rare earths and many highly ionized atoms are largely unexplored. However the spectra of Fe I, II and III are now fairly well analysed.