Since the recovery in October 1982, an extensive, international programme to observe Comet Halley with ground-based instruments has been co-ordinated by the International Halley Watch (IHW), and a comprehensive archive is now in the final phases of preparation. The observations were carried out at more than 150 observatories and with all available methods. A special effort was made to support the space missions during the comet encounters in early March 1986. Whereas the spacecraft provided detailed in-situ measurements over a short time interval, ground-based observers have so far followed the development of the comet over a period of nearly six years, and a number of spectacular events near the nucleus and in the tail have been documented in great detail. These observations still continue. This article gives an overview of the most important results obtained from the ground and also mentions the prospects for further observations with large telescopes during the next years.

An international armada of spacecraft encountered Comet Halley in March 1986. The present article gives a brief overview of this unique event during which a cometary nucleus was seen as a spatially resolved object for the first time. It is a very dark body, the shape is irregular and the structure is inhomogeneous; only the sunward side is active. Many parent molecules were identified in the coma, including complicated hydrocarbons. There was also organic matter in the comet dust particles. Extensive studies were made of the complicated plasma environment of the comet.

It is a great honor for me to speak to you tonight on the subject of quasars. In the past twenty-five years, an enormous amount has been learned about these objects and the field has become very technical. I recognize that there are many people in the audience who are not professional astronomers and I hope not to disappoint them. At the same time my colleagues may recognize a few things that I touch upon. They will also hopefully forgive me for leaving out many attributions: many hundreds of astronomers have contributed to the field.

My aim in this general talk will be to air some questions, rather than offer firm answers, because the most basic questions about galaxies are indeed still unresolved. In particular:

1. We do not know why such things as galaxies should exist at all — why these assemblages of stars and gas with fairly standardised properties are the most conspicuous large-scale features of the cosmos.

2. About 90% of the mass associated with galaxies is hidden. The luminous stars and gas contribute only about a tenth of the gravitating material inferred from dynamical arguments. What the rest consists of is still a mystery.

3. It is unclear why the nuclei of some galaxies flare up, and release the colossal amount of non-stellar radiation emitted from quasars and radio galaxies, as discussed by Maarten Schmidt in his discourse.

The meeting provided a forum in which those responsible for documentation and data services in astronomy could interact with users of these services in an endeavour to establish how new techniques for the distribution and retrieval of information may be used to best advantage by astronomers. The report contains summaries of each of the short papers that were presented during the four sessions and brief accounts of the ensuing discussions. The principal topics were: the preparation and publication of papers and reports; bibliographic data services; electronic-mail facilities; archiving of current observational data; the changing role of libraries; and the maintenance of the historical record of astronomical activities.

A small fraction of the enormous volume of records that are generated by research and development activities should be selected for permanent retention because of their potential value to future scientists, engineers, historians and others. The records are generated for many different purposes and in many different forms (not all are documents). There are, however, some basic principles that should be used in appraising the records so that the most appropriate of them are selected according to identifiable criteria.

New observations of binaries are beginning to provide new clues on the formation and evolution of binary and multiple systems in a variety of stellar populations in the Galaxy. New orbital determinations are shedding light on the frequency and orbital characteristics of binaries in the disk and the halo of our Galaxy, both in clusters and the field. These results support the view that the formation of binaries involving solar-mass stars is relatively independent of the stellar environment. Evolutionary effects can have a major influence for close binaries with periods up to at least ten days, with a strong dependence on the age of the population. Progress towards determining the frequency of low-mass companions and planetary systems is promising but still very limited.

Nine of 18 stars observed with a high precision radial velocity technique show long term, low level variations which imply the presence of companions in the range of 1 to 10 Jupiter masses. These companions could represent the tip of the planetary-mass spectrum.

Although the unusual nature of T Tau was noted over four decades ago, the first orbit for a low-mass pre-main sequence (PMS) spectroscopic binary was not determined until Mundt et al. (1983) serendipitously discovered the double-lined nature of V826 Tau. To some degree the paucity of spectroscopic binary detections may be attributed to the faintness of such stars and the consequent difficulty in obtaining high resolution spectra; the first high-precision radial-velocity survey was that of Herbig (1977). Advances in radial-velocity measurement technology now permit relatively easy velocity measurements of PMS stars. However, V826 Tau was also one of the first discovered members of the naked T Tauri (NTTS) class of PMS stars (Walter 1987) and its discovery as a spectroscopic binary foreshadowed a prevalence for binary detection among this population. In this short paper we review the present observational status of PMS spectroscopic binaries and present several initial results and thoughts for consideration.

The lunar occultation technique applied in the IR offers a powerful means of identifying binaries among obscured young stars. Our program has revealed binaries with separations from 1 to 100 AU in the Taurus and Ophiuchus star forming regions to about K=9 mag. To date, 29 objects have been observed; 6 were discovered to be binaries. The observed binary frequency is about half that expected from the binary statistics of a comparable sample of field stars. The discrepancy is probably attributable to our insensitivity to binary systems with secondary mass much less than that of the primary.

Searches for brown dwarf companions to known stars have revealed a number of tantalizing candidates.

Interstellar clouds are thought to undergo a rapid phase of collapse in the process of contracting to form stars. Break-up during this collapse phase is termed fragmentation. Computer codes capable of calculating the hydrodynamics of cloud collapse in three spatial dimensions have been used to study the fragmentation process. Fragmentation into binary or multiple protostellar systems is the preferred outcome of collapse; only very slowly rotating, high thermal energy clouds, or clouds starting from power-law initial density profiles, avoid fragmentation and form single stars.

Three dimensional computations for processes of collapse and fragmentation of rotating gases are performed and criteria for fragmentation of rotating clouds in the cases of the various equation of state are obtained.

A review is given of the current mathematical and theoretical status of the possibility of the formation of binary stars by fission. It is emphasized that none of the competing theories is completely deductive: each begins with a preconception of how fission might occur, and considers mathematical problems that bear on the viability of that preconception. The classical fission theory turned out to lack internal consistency. The present author’s version of the theory, revised from the classical theory in that viscosity plays a negligible rather than a dominant role, appears to be internally consistent and compatible with the idea that close binaries with mass ratios near one may form in this way. The version of the theory described elsewhere in this volume by Durisen, which fails to produce binaries, is based on a preconception of the route to fission different from the classical one. Its failure to produce binaries therefore reflects only on that route, and not on other possible routes to fission.

Recent hydrodynamic simulations indicate that gravitational torques due to spirals arms suppress binary fission in rapidly rotating polytropic fluids.

For a given mass M and environmental temperature T, there is a well-defined angular momentum Jmax above which physical systems cannot exist as self-gravitating entities. The quantity Jmax α M2 T−½. Observations of J and M in young binary systems should put useful constraints on the temperature of the medium from which they formed.

The number density of stars in the cores of globular clusters is high enough for close encounters between stars to be frequent. These encounters may lead to the formation of binaries. Those binaries which do not easily form via the evolution of primordial main-sequence star binaries, and are therefore rare in the galactic disk, can be common in globular clusters. Examples of such binaries are the low-mass X-ray binaries. Such binaries may evolve into radiopulsars.

The dynamical processes of formation, evolution and disruption of binaries may be effectively studied by computer simulations in the N > 3-body gravitational problem. As a result of analysis of these investigations of diverse authors, the classification of the dynamical processes of formation of wide and close binaries may be proposed (see Table 1). This Table shows the following general processes: I-triple approaches of the single bodies; II-approaches of binaries with single bodies; Ill-escape from physical triples. The actions of these processes, and kinetics of a frequency of binaries in general field were studied at the Astronomical Observatory of the Leningrad State University (1965-1988) by computer simulations in the three-body problem. More than 3.104 orbits with negative total energy E < 0 and 5.104 with E > 0 have been run on the computers. The film “Dynamical evolution of triple systems” was produced. Part I of this movie shows the evolution of the unstable non-hierarchical triplet as well as the processes of formation, evolution, and disruption of temporary wide and final close binaries inside the physical triples. Part II of film presents in detail the trajectories of the bodies on the triple approaches of “fly-by”-and of “exchange”-types. The triple approach of “fly-by”-type results often in an escape from triple as well as the formation of final close binary. The triple approach of “exchange”-type consists as a rule of a few close double approaches of bodies and rarely results in an escape from triplet, it results in formation of temporary wide binary inside triplet. Part III of movie presents the trajectories of the different-mass bodies: an escape of the minimum-mass body, the intermediate-mass body, and the maximum-mass body as well as a formation of binaries with different-mass components.

The use of binary systems as tools for testing models for single-star (“undisturbed”) evolution is briefly reviewed. Recent successes and directions for future work are discussed.