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 Inaugural Ceremony was held at the Convention Center, Baltimore, in the presence of distinguished representatives from the Government of the United States, the State of Maryland, the City of Baltimore, the Johns Hopkins University, the National Aeronautics & Space Administration, the and the US National Committee for the IAU.

The chair was taken by Dr. A. Davidsen, co-Chairman of the Local Organizing Committee, from the Johns Hopkins University.

A rousing aubade, specially composed for the occasion by Elam Ray Sprenkle, was beautifully performed by the Annapolis Brass Quintet under the direction of David Cren.

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).

An Extraordinary General Assembly was held immediately preceding the first session of the General Assembly on 1988 August 2 to amend the Statutes of the Union to permit the election of a President-Elect to the Executive Committee and to institute a new category of adherence to the Union-Associate National Member status for countries in the process of developing astronomical activity.

Je voudrais commencer cette première séance de la Vingtième Assemblée Généale de l’Union Astronomique Internationale en vous souhaitant d’une part la bienvenue et, d’autre part, un séour non seulement très agréable mais surtout très profitable au point de vue scientifique.

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.

It was the President’s sad duty to report the deaths of two former past Presidents of the Commission, W. Fricke who had also been a Vice-President of the IAU and a President of Commission 8, and D. H. Sadler who had been Superintendent of H.M. Nautical Almanac Office from 1936 to 1969 and was once General Secretary of the IAU.

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.