The complex flare related events taking place in the solar corona are becoming better understood as more observations are made with high spatial and temporal resolution nearly simultaneously at widely separated radio frequencies. Similarly the magneto-plasma structures related to the so-called quiet Sun, which have been extensively studied during the recent cycle (No. 20), are now better understood because of such high resolution observations.

Whether a mechanism for the emission of radiation can properly be regarded as thermal or non-thermal depends on the nature and extent of the interactions that take place between the radiation resulting from such a process and the surrounding medium. Thus, no matter what the emission mechanism there can be a balance between emission and absorption processes such as to produce a state of local thermodynamic equilibrium (LTE), so that the net radiation available for transport through the source region is thermal.

Pulsars are unique astronomical objects in that their emission is in the form of a periodic pulse train. For most pulsars the pulse duty cycle is small, only a few per cent of the period. The shapes and intensities of individual pulses are in general quite variable. This is illustrated in Figure 1 which shows a series of individual pulses from PSR 1133 + 16. Despite this variation in shape of individual pulses, it is found that the mean or integrated pulse profile obtained by adding many pulses synchronously with the period is in most cases stable in shape.

The UK 1.2 metre Schmidt Telescope came into operation in 1973 with the primary purpose of extending to southern declinations the Sky Survey carried out with the Palomar 1.2 metre (48 inch) Schmidt Telescope. This telescope is, in most respects, an exact copy of the Palomar telescope, but several recent developments result in a much fainter limiting magnitude (by about 2 magnitudes) for the Southern Survey. The UK Schmidt Telescope has an aperture of 1.2m, and the spherical primary has a diameter of 1.83m and focal length 3.07m. The plates have the dimensions 356 x 356mm, giving a field of view of 61/2°; the plate scale is 67″ 1/mm.

It is impossible in half an hour to do justice to the vast literature on Shockwaves in interstellar space. Here, an attempt is made to identify outstanding problems with particular regard to the optical spectrum and to determine what physical data can be relatively unambiguously obtained from interpretation of this.

Detailed physical mechanisms responsible for excitation of spectral lines in gaseous nebulae have been known for 50 years, and reasonable estimates of nebular densities and temperatures were obtained in the late thirties and early forties. However quantitative chemical analyses have proven difficult partly because of uncertainties in atomic parameters (notably collision strengths) and partly because of complications posed by the nebulae themselves.

A white dwarf is a body of stellar mass, but of planetary dimensions. It is self luminous with a surface temperature that has been observed as high as 70,000 K or as low as 4,000 K. Because of its low surface area the star is far fainter than a main sequence star of the same colour; equally the light it emits is bluer than that from a main sequence star of similar luminosity. Figure 1 is the HR diagram from data obtained by the US Naval Observatory showing the dwarf and white dwarf sequences.

Since their initial discovery by Hale, the nature of solar magnetic fields has presented us with a number of problems. At one time it was thought that the field consisted of a weak background dipole field of order 1-2 G on which was superimposed the considerably more intense fields associated with active regions and sunspots. However, more recent observational studies by Harvey, Frasier, Stenflo and others have suggested that 90% of the background field appears in the form of intense small-scale fields with intensities of order 103 gauss or greater and which have remarkably similar properties whether they occur in active or quiet regions. In particular, the field intensity appears independent of the total amount of flux present but the appearance of the structure depends critically on the total flux.

According to Oort (1965), the mass density in the solar neighbourhood (inferred from the gravity component normal to the galactic plane) is between 50% and 150% greater than the mass density inferred from non-dwarf stars. One possible explanation for the “missing mass” is an overabundance of faint M-dwarfs (Weistrop 1972), but present indications are that this overabundance is either small (Weistrop 1976; Sanduleak 1976) or non-existent (Faber et al. 1976; Eggen 1976). Nevertheless, Salpeter’s initial mass function (Salpeter 1955) suggests that the total mass may be dominated by low mass stars, including masses M≤0.08M⊙ which never undergo significant hydrogen burning.

Some self-absorbed synchrotron sources have, a small but observable degree of circular polarization rc near the absorption turnover (Roberts et al. 1975). The simplest interpretation of the circular component is in terms of the intrinsic degree of circular polarization of synchrotron radiation (Legg and Westfold 1968); this provides a relation (Roberts et al. 1975)

Stewart (1978) has reported four moving type IV bursts observed with the Culgoora radio heliograph at 43, 80 and 160 MHz. After an early phase, the brightness temperatures of the observed bursts decreased with increasing frequency and with time. The highest brightness temperature observed at 43 MHz was 1010K, and it seems that the brightness temperature would have been still higher at even lower frequencies. Existing theoretical ideas on moving type IV bursts are based on data (at 80 MHz primarily) which included no brightness temperatures in excess of 109K. the accepted interpretation involved gyro-synchrotron radiation from mildly relativistic electrons (energies ≈ 100 keV); reabsorption by the electrons themselves restricts the brightness temperature to less than about 100 keV ≈ 109K (Wild and Smerd 1972, Dulk 1973). Stewart’s (1978) new data at 43 MHz require that this accepted interpretation be modified; he has suggested that higher energy electrons are involved. An alternative suggestion is explored here, namely that the absorption might be negative. In other words, the high brightness temperatures observed could be due to a gyro-synchrotron maser involving electrons with energies of about 100 keV.

Recently (Gleeson (1972), Quenby (1973), Gleeson and Webb (1974, 1978)) it has been shown that the mean rate of change of momentum of cosmic rays reckoned for a volume fixed in the solar system is

where G = (1/Up)(∂Up/∂r)si the cosmic-ray density gradient with Up, the differential number density with respect to momentum p at position r. (cf also the integral form of (1) by Jokipii and Parker 1967).

The arms in spiral galaxies cannot be material arms for then they would wind up on a time scale of one galactic rotation, or a few times 108 years. The large number of spirals suggests that the spiral pattern must persist for about 1010 years (or be continually rejuvenated). The density wave theory treats the spiral pattern as a wave phenomenon, thus overcoming this problem. Much work has been done studying small amplitude oscillations in flat stellar discs. Self-consistent spiral modes have been found, but they are not stable and grow at a fast rate. Numerical simulations of thin stellar discs, such as those of Hohl (1971), which can handle finite amplitude waves, have been more successful. Spiral waves form initially but evolve into a steady state rotating bar. It seems therefore, that a long-lived spiral cannot be formed in stars alone.

Lin and Hudson (1976) have recently analysed non-thermal processes in proton flares, using observations of a series of major events in August 1972. They concluded that the 10–100 keV electrons accelerated during the flash phase account for the bulk of the total energy of a large proton flare (about 1032 – 1033 ergs); that most protons are accelerated later than the 10 — 100 keV electrons; and that most energetic protons escape to the interplanetary medium. Their conclusions with regard to proton acceleration are supported firstly by the delay of the maximum of γ-ray emission by 3-5 minutes after the maximum of X-ray emission, and secondly by the satisfactory agreement between the 7-ray spectrum and the thin-target model of emission. The energetic protons contain a very small fraction of the total flare energy (of the order of 10-5).

Solar flares for which protons of relativistic energies reach Earth are rare events compared with the number in which non-relativistic protons are produced. For instance, Shea and Smart (1978) have listed 139 proton events for the interval 1955-69 of which 17 were GLE’s (i.e. “ground level events” detected by the world network of cosmic ray neutron monitors). We have tentatively identified a further 11 GLE’s in the interval 1970-1977, of which 3 were in 1977 in the sunspot cycle which commenced about mid-1976 (cycle 21). Thus the average rate over the past two solar cycles has been a little over one per year.

During the Skylab period from June 1973 to January 1974 approximately 1500 type III metre-wave radio bursts or burst groups were reported (Solar Geophysical Data Prompt Reports). The longitudinal distribution of these type III bursts closely resembles that of sunspots and of the coronal transients observed above 2 R⊙ by the white-light coronagraph on Skylab. White light ejection transients appear as large loop or blob-like structures which carry material outward from the Sun and rearrange the corona. In front of the main, bright structures there are weak enhancements of brightness, termed forerunners (Jackson and Hildner 1978; Jackson 1978). In this paper we enquire into whether or not type III bursts are in any way related to the onset of solar mass ejections indicated by coronal transients.