This report covers the period from 1 July 1984 to 30 June 1987. The ephemerides that have been published during this period have made use of the new system of astronomical constants adopted at the XVIth General Assembly of the lAU in Grenoble. Yet some difficulties have arisen because of the lack of catalogues or maps of the heavens established for the epoch J2000.0. This is awkward for observers of comets and minor planets and, for that reason, Commission 20 decided, at the New Delhi meeting of lAU that there would be a gradual introduction of the J2000.0 system as far as those bodies are concerned.

The aims of this report are, firstly, to review the activities of Commission 5 during the period since the IAU General Assembly in Delhi in November 1985 and, secondly, to draw attention to other relevant activities. It is based mainly on contributions from the Chairmen of the working groups and other members of the Commission, but it also includes some items of general interest that have been taken from the Commission’s Newsletter. The Working Groups and their Chairmen are as follows:

The commission has been able to continue its work during the last triennium with a minimum of effort. Thanks for this and for the untiring dedication are due to the Director of the Bureau, B. G. Marsden. We are also grateful to the Smithsonian Astrophysical Observatory for its general support.

According to the annoucement published in the IAU Information Bulletin no 58, K. A. Thernöe died on 1987 March 7. He was the director of the Central Telegram Bureau during the years 1960 - 1964 in Copenhagen and for many years he served as principal substitute for Julie Vinter Hansen when she ran the Bureau.

During 1985-1987 Celestial Mechanics has been intensively developed in all its branches embracing physical bases, mathematical aspects, computational techniques and astronomical objectives. Commission 7 has organized three IAU conferences: Symposium No. 114 “Relativity in Celestial Mechanics and Astrometry” (Leningrad, May 1985), Colloquium No. 96 “The Few Body Problem” (Turku, June 1987) and Topical Session “Resonances in the Solar System” of the X-th European Regional Astronomy Meeting (Prague, August 1987). Members of the commission have broadly participated in the NATO Advanced Study Institute “Long-Term Dynamical Behaviour of Natural and Artificial N-Body Systems” (Cortina d’Ampezzo, August 1987) and some other international and regional conferences. Prospects of the actual celestial mechanics investigations have been discussed at a session of Commission 7 at the XIX-th IAU General Assembly (New Delhi, November 1985). Three papers dealing with the unsolved problems of celestial mechanics were primarily addressed to the rising generation of celestial mechanicians (V. A. Brumberg and J. Kovalevsky, CM. 39, 133, 1986; P.K. Seidelmann, CM. 39, 141, 1986).

The Commission deeply regrets the death of our colleague G. Teleki who passed away on February 1987.

After the retirement of T. Dambara, S. Lautsen and W. Gliese and the arrival of C. Turon-Lacarrieu as a new member, the membership of our commission is 142.

The technology leading to very large aperture telescopes and their optics has progressed well in the period since 1984 and plans for many new large aperture telescopes have been made. Focal plane instrumentation continues to become more sophisticated or more efficient: multi-object capabilities, automatic instrument control and operation, and increasing use of CCDs are examples of areas to which this applies. The proportion of time devoted to observations using two-dimensional photoelectronic detectors has grown substantially at many observatories, particularly with telescopes of moderate aperture; and the use of high quantum efficiency array detectors is now being extended into the infrared spectral region. Important advances have also been made in instrumentation and techniques for ground-based high angular resolution interferometry.

In preparing the present report, which covers the period July 1, 1984, to June 30, 1987, close collaboration has taken place between Commission 10 and 12, the two solar commissions, in order to avoid duplications and to insure that pertinent subjects are treated. The reader is referred to the report of Commission 12 for further solar topics. The proceedings are found at the beginning of the references for each section, followed by the usual alphabetical listing. In some sections this listing refers to the previous proceedings by their numbers; in others we retain the conventional reference. It is a pleasure to acknowledge the excellent work of the reviewers who wrote the different sections of this report, and all the members of the commission who provided information on research to be included.

The development of research on starspots, stellar activity, and the suspected relationship between coronal heating and magnetic field have reenforced the interest of the study of the solar magnetic field and the study of the associated thermodynamic structures. Several proceedings of scientific meetings appeared from 1984 to 1987 (Measurements of Solar Vector Magnetic Fields, 1985 (I); The Hydrodynamics of the Sun, 1984 (II); High Resolution in Solar Physics, 1985 (III); Theoritical Problems in High Resolution Solar Physics, 1985 (IV); Small Scale Magnetic Flux Concentration in the Solar Atmosphere, 1986 (V)). The finding that the solar irradiance in affected by solar activity has renewed interest in photometry of sunspots and faculae. Sunspots have been used for investigating solar differential and meridional motions. Some results are also found in Section III.

During the past three years arguments related to the AR physics can be found in the proceedings of the following meetings: Chromospheric Diagnostics and Modelling, NSO Sacramento Peak, 1984 (I); The Hydromagnetics of the Sun, Noordwijkerout, ESA, 1984 (II); Solar and Stellar Physics, Titisee, 1987 (III). Many aspects concerning the high activity levels of AR’s can also be found in the proceedings of large number of meetings organized on solar flares. Microwave mapping is reported in Section VII. Some results are also reported in Section II.

This report is a summary of the work done on the physics of prominences and filaments. An overview of modern observations has been written by Hirayama (1985). The behaviour of solar Coronal and Prominence Plasmas (CPP) has been the topic of two SMM meetings, organized by A. Poland in 1985 and 1986, in Goddard Space Flight Center. An extensive review of the subject (formation, spectroscopic diagnostics and instabilities, with a large amount of contributed papers) can be found in the proceedings (Poland, 1986 (I)). Also, the physics and the structure of prominences will be discussed, from a more theoretical point of view, during a next workshop, in Palma de Mallorca, organized by E. Priest and J.L. Ballester in November 1987.

The basic results of the SMA were presented and summarized in two SMA Symposia Proceedings, edited by Simon (1984 (I) we will refer to this publication using abbreviation SIM) and by De Jager and Svestka (1986, DJS (II)). Other papers discussing SMA results can be found in Proceedings of SMM Workshops (Kundu and Woodgate, 1986 - KAW (III); Poland, 1986 - POL (IV); Dennis et al., 1987 (DOK (V)) and three other meetings held at Kunming (De Jager and Chen Biao, 1985, JCB (VI)) Irkutsk (Stepanov and Obridko, 1986 (SAO (VII)) and Sacramento Peak (Neidig, 1986, NEI (VIII)). A summary of Soviet contributions to the SMA (until 1985) was prepared by Stepanov (in SAO, p. 5). Kindly note that this Section does not mention most of the SMA results that belong to the topics of the subsequent sections of this report: thus the SMA results of space observations should be found in Section VI, radio observations in Section VII, etc. The present report will be mostly limited to those results of the SMA which use or interpret optical ground-based data.

Although the solar activity began to decrease rapidly after 1983, the analysis and interpretation of the observations made with instruments aboard the SMM, Hinotori, P78-1, ISEE-3 (ICE), PVO, Venera, and PROGNOZ spacecraft continued to produce important scientific results. The observational results inspired new theoretical studies or extensions of the earlier studies. Several symposia and workshops were organized for presentation and discussion of coordinated studies or studies in progress.

This section does not mention some results reported in sections V and VI. Other papers can be found in proceedings of CESRA Workshops (Benz 1985 (I), Pick and Trottet 1986 (II)).

By far the most significant event for Solar Flares as a whole over the past 3 years has been the operation of the Solar Maximum Mission Satellite, together with the accompanying data analysis, ground-based support and theoretical modelling. This has culminated in the series of SMM Flare Workshops, whose proceedings have now appeared (Kundu and Woodgate 1986 (I)), with chapters on a wide variety of topics which indicate the enormity and complexity of the flare problem.

Solar Physics has been traditionally divided into Structure and Radiation of the Solar Atmosphere (commission 12) and Solar Activity (commission 10). There has been increasing evidence that solar activity, which is basically of magnetic origin, occurs on a great variety of scales arid thus immediately touches upon the structure of the solar atmosphere as well as the structure and dynamics of the convection zone. As a consequence progress in the field of origin and evolution of solar magnetic fields from a large scale, ‘the dynamo’, to small scale is included in this report. In the past few years particular attention has been paid to the fact that the fluctuations in the magnetic field are much larger than the mean field and that the dynamo modes may be stochastically excited. The question whether there is a magnetic reservoir at the bottom of the convection zone still remains to be resolved. The interaction of the convection and the magnetic field resulting in an enhancement of the magnetic field in the intergranular lanes is studied by numerical modelling.

Traditionally the theory of the solar dynamo has been divided into two parts. The first, more difficult part, is the derivation of equations governing the mean magnetic field; the second, easier, is the solution of this equation, and the interpretation of the result in terms of observed solar magnetism. This report follows the traditional division.

Considerable progress has been made during the last four years in the theoretical and empirical investigation of the small scale solar magnetic field and associated phenomena. Although the basic outlines established in the 1970s of the structure of the field, namely small fluxtubes or magnetic elements with kllogauss fields embedded in a relatively field free medium have survived, many of the details have changed and some of the large gaps in our knowlegde of these captivating structures have been filled. In the following we briefly outline some of the highlights.

The crucial role of magnetic fields in any mechanism to heat the outer solar atmosphere has been generally accepted by all authors. However, there is still no agreement about the detailed function of the magnetic field. Heating mechanisms can be divided up into 4 classes: (I) The magnetic field plays a passive role as a suitable medium for the propagation of Alfvén waves from the convection zone into the corona (Ionson, 1984). (II) In closed magnetic structures the slow random shuffling of field lines by convective motions below the surface induces electric currents in the corona which heat it by Joule dissipation (Heyvaerts and Priest, 1984). (Ill) Emerging flux which is generated in the convection zone reacts with ionized material while magnetic field lines move through the chromosphere, transition zone and corona. Rapid field line annihilation, reconnection and drift currents result in heating and material ejection (Brueckner, 1987; Brueckner et al., 1987; Cook et al., 1987). (IV) Acoustic waves which could heat the corona can be guided by magnetic fields. Temperature distribution, wave motions and shock formation are highly dependent on the geometry of the flux tubes (Ulmschneider and Muchmore, 1986; Ulmschneider, Muchmore and Kalkofen, 1987).

Studies of the global (spatially unresolved) output from the sun are important for two main reasons: (1) the global solar output directed towards the earth plays a central role in solar-terrestrial relations, and (2) global solar observations form a link between (neccessarily) global observations of stars and the more refined spatially resolved observations which are available for the sun. This report covers both aspects (insofar as they concern the sun), using the time-scales of various phenomena as a basic distinguishing characteristic. Note that certain studies of spatially unresolved solar output have not been discussed, since they are actually directed toward the investigation of phenomena of strictly limited spatial extent [e.g. radiospectrograph observations (e.g. Wiehl et al. 1985) and studies of X-ray bursts (e.g. Thomas et al. 1985)]. Collections of relevant papers may be found in De Jager and Svestka (1985) and Labonte et al. (1984), while a review of germane stellar work is available in Baliunas and Vaughan (1985) and solar-terrestrial work in Donnelly and Heath (1985). A comprehensive summary of the subject by Hudson will appear soon in Review of Geophysics and Planetary Physics.

This report complements the report on solar instrumentation presented by Commission 10 In that subjects treated there are not repeated here. Both reports taken together should give a fair, though necessarily incomplete, idea of solar instrumentation activity during the period June 1984 through June 1987.