As before a number of authors have contributed reviews of their own field. The contributions were editted by the President in order to avoid some overlaps, to reduce the length of the reviews and to add some publications. Reference numbers from “Astronomy and Astrophysics Abstracts” were used when available. In the end of the report a list of references not found in “Abstracts” is given. As editor, the President takes the responsibility for any shortcomings in the report.

One of the continuing problems facing Commission 24 is its name. It has been known and reported for some years that the present title is not suitable for reasons that are all too obvious. This problem has continued during the last three years, despite the growing development and use of non-photographic methods and techniques.

Most of the recent meeting activity in which the Commission and its membership has been involved, has centered on its shared interests with Commission 8 and with the Working Group on reference frames formed at the last General Assembly. Since its inception at that time, C. A. Murray has been appointed to represent the Commission on that group.

The outstanding feature of the last triennium was most certainly the abrupt generalisation of the use of array detectors, particularly CCDs (charge coupled devices). The latter pervade all subdivisions of instrumental astronomy. The gains achieved by their high quantum efficiency, their stability, their capability of delivering immediately recordable signals which can be processed by appropriate computational means, have been the cause of spectacular progress regarding the photometric precision of weak signal measurements.

In the recent years new techniques are expanding visual binary star astronomy into previously inaccessible regimes of angular resolution and accuracy of measurements regarding the astrometric and astrophysical parameters of their components. New techniques and algorithms are providing enhanced sensitivity to low mass companions and the determination of photometric properties of the components of close visual binaries. The potential now exists for significantly narrowing, if not eliminating entirely, the historic gap separating spectroscopic from visual binaries. Advances in closely related fields as in precision radial velocity measurement and enhanced accuracy of parallax determination from ground and space based observatories will place demands upon double star astronomy that have been absent for half a century. Today double and multiple star astronomy is perhaps closer to fulfilling its true potential than it has ever been, entering a fundamentally important area of modern astrophysics.

The field of variable star research has become so broad and the amount of research to be reported on has grown so rapidly that it is a vain hope that a report of this kind, in a very limited space, could cover the whole field of research and could mention all the papers that have been published in the last three years. It is only hoped that this report presents the significant results achieved in the field of the most important aspects of variable star research. Some important subjects (e.g. cataclysmic variables) relevant to the variable star research are reviewed in the reports of other commissions. This is a consequence of the fact that the research has become very complex and the phenomena producing light variability belong to the field of interest of other commissions, too.

This report covers the period 1 July 1984 to 30 June 1987 and - as usual - has been prepared by the President, Vice-President, members of the Organizing Committee and the chairpersons of the Working Groups. There has been emphasis on highlights rather than on completeness of references. In comparison with earlier reports one section (Galactic Dynamics) has been added, but otherwise the same line of reporting has been used. For readability and quick reference, in general abbreviated notation for literature references to major journals have been used; more complicated ones usually follow the code of Astronomy and Astrophysics Abstracts. The abbreviation et al. has been replaced by the symbol +.

In the triennium under review, from the second half of 1984 to the first half of 1987, Commission 29 has sponsored or cosponsored the following IAU Conferences: Symp. 120, “Astrochemistry”, GOA, India, December 1985; symp. 122, “Circumstellar Matter”, Heidelberg PRG, June 1986; Symp. 132, “The impact of very high S/N Spectroscopy on Stellar Physics”, Paris, France, June-July 1987; Symp.123, “Advances in Helio and Asteroseismology”, Aarhus, Denmark, July 1986; Coll. 87, “Hydrogen Deficient Stars and Related Objects”, Bangclore, India, December 1985; Coll. 88, “Stellar Radial Velocities”, Schenectady, N.Y., U.S.A., October 1984; Coll. 90, “Upper Main Sequence Stars with Anomalous Abundances”, Crimea, May 1985; Coll. 92, “Physics of Be Stars”, Boukder, CO, U.S.A., August 1986; coll. 94, “Physics of Formation of Fell Lines Outside LTE”, capry, Italy, July 1986; Coll. 95, “Second Conference on Faint Blue Stars”, Tucson, AZ, U.S.A., June 1987; Coll. 102, “UV and X Ray Spectroscopy of Astrophysical and Laboratory Plasmas”, Beaulieu-sur-Mer, France, September 1987; Coll. 108, “Atmospheric Diagnostic of Stellar Evolution: Chemical Peculiarities, Mass Loss and Explosion”, Tokyo, Japan, September 1987.

The present report on the activities of IAU Commission 30, covering the triennium June l, 1984 through June 1, 1987, will be somewhat different from its recent predecessors in both content and style. Over the preceding decade or so, the reports mainly emphasized the dramatic improvements in observing efficiency, achieved primarily through the general adoption of cross-correlation techniques, combined with modern detectors attached to either specialized spectrometers or to existing, more conventional instruments. A great surge of observational activity followed, directed towards a variety of astrophysical problems, some of which are of a more classical nature, but many of which are in entirely new classes of research. At the time of the previous reports, most of the major observational projects were still underway, even if some preliminary results were emerging. The proceedings of IAU Colloquium No. 88, Stellar Radial Velocities (L. Davis Press, 1985) contains a collection of papers on instrumentation and reduction techniques as well as on ongoing observing programs which remains a very useful source of references to this developmental phase as well as to the current state of the art.

The work of IAU Commission 31 members is contained mainly in the reports contributed by members and listed below. Unfortunately because of limitations in space, journal references to the work could not be listed. Readers interested in any of the topics mentioned in the reports are urged to contact those who have submitted that particular report for further information.

During the period from 1984 to 1987 the membership list of Commission 31 was revised to reflect new addresses and telephone numbers. Those listed as members previous to this period who were no longer concerned with Commission matters were deleted from membership. Members were also asked to submit their recommendations for future research in the area of time. The result of this poll was the formation of two working groups.

Commission 33 has the long-standing tradition of producing two versions of the report covering its activities in the general field of Galactic Structure during the past triennium. The short version of the report is the one presented here. A longer, more complete version, is being printed by the President for distribution to all members of the Commission.

Compilation of the triennial summary is one of the major tasks of Commission officers. Section 2 of this report was prepared by M. Major; section 3 by L. Balasz; sections 4 and 8 by L. Blitz; section 5 by G. Lynga; section 6 by D. Hartmann; section 7 by J. Bloemen; sections 9 and 10 by U. Haud and J. Einasto; section 11 by R. Wielen; section 12 by B. Puchs; section 13 by J. Binney; and section 14 by V. Malyuto and J. Einasto.