The Commission has, since its inception, been devoted to the continually increasing needs of astronomy and astrophysics for reliable atomic and molecular data a) for diagnostic interpretation of astronomical observations, and b) for support of theoretical modelling of astrophysical situations. At the 1985 Delhi General Assembly, the Commission reviewed the scope of its subject matter, and considered whether it should be extended to include higher energy physical processes than are commonly treated by atomic and molecular data. It was concluded that there was no strong demand for this change, which, if implemented, would make the work of the Commission too diffuse. The appropriateness of the past working group structure was also carefully reviewed in the light of contemporary needs. The following working groups, which have evolved from those of past years, together with their chairmen was approved:

1. 1: Atomic Spectra and Wavelength Standards (excluding primary standards): W.C. Martin

2. 2: Atomic Transition Probabilities: W.L Wiese

3. 3: Collision Processes: A. Dalgarno

4. 4: Line Broadening: N. Feautrier

5. 5: Molecular Structure and Transition Data: W.H. Parkinson

The Data Center on Atomic Transition Probabilities at the National Bureau of Standards, Gaithersburg, Maryland, 20899, U.S.A. has continued its critical compilation work and maintains an up-to-date bibliographical data base. Work to revise and expand the existing NBS critical data compilations for the allowed and forbidden transitions in Fe-group elements, (Refs. A-D) has been completed. A single volume containing all these data for the Fe-group elements Sc to Ni is in press (Volume III of the NBS series of atomic transition probability tables) and is scheduled to be published in the near future, as a supplement to the Journal of Physical and Chemical Reference Data.

Of the vast array of data on electron and heavy-particle collisions that are produced each year, I select only those that have an obvious immediate bearing on astronomical research. A brief review of recent developments in atomic data for astrophysics has been published (1).

There has been quite a renewal of interest in the field of line broadening during the last three years and the proceedings of the Eight International Conference on Spectral Line Shapes (1) showed the general state of progress of this topic. It is not the purpose of this report to be exhaustive, so we will simply give a number of useful results for astrophysical purposes and indicate some new fascinating directions in this research theme.

Research in molecular spectroscopy has continued to grow over the past three years. The spectral range has expanded from the far ultraviolet to millimeter wavelengths. The report has been limited to molecular spectroscopy of relevance to astronomy and has been compiled from edited contributions sent to me in the fall of 1987.

The period covered by this report, 1984 July to 1987 June, was of extraordinary importance for the progress of cometary physics. For the first time in the history, special space probes were launched to comets. Vega 1, Vega 2 and Giotto encountered P/Halley, providing us with the first close-up pictures of a cometary nucleus, its surface features, and with the first in situ measurements of the matter escaping from it. ICE, Suisei and Sakigake carried out measurements relevant to P/Giacobini-Zinner and P/Halley in interplanetary space. Unprecedented worldwide campaigns of ground-based observations, with the participation of about 1000 professional and 2000 amateur astronomers, were coordinated in 8 sections of the International Halley Watch. Additional measurements were made from artificial satellites, sounding rockets, and highflying airplanes. The wealth of data collected in this way, to a major extent thanks to an excellent international cooperation, represents a milestone in cometary astronomy. Another important step was the progress in processing the extensive 1983 IRAS observations of minor planets and comets, including the discovery of asteroid dust bands and cometary dust trails.

The physical study of planets and satellites is probably one of the more active fields of research of the second half of this century. This is due to space exploration by spacecraft, but also to the use of modern detectors, of large ground-based telescopes, and of powerful computers by active researchers. Planetary research (or planetology) is a pluridisciplinary domain, which requires not only the competence of astronomers, but also of geophysicists, of mineralogists, of climatologists, of biologists, of chemists, of physicists, of “pure„ mathematicians, and many other scientists. Many results are at the boundary of those of other commissions such as the 15, 20, 7, 19, 33, 40, 44, 49 and 51 ones. The study of the main results obtained during this last triennum shows a perfect complementarity between space and ground-based observations. It should be arbitrary to separate space and ground-based scientists. The have the same goal and they study the same objects. Quite often, the same individuals use both techniques, depending on the most efficient one for the problem under study. It is remarkable to see that space data collected more than ten years ago are still analysed in connection with ground-based observations. The same remarks can apply for ground-based data. In addition to that, new theoretical models, new numerical simulations and new laboratory experiments have ben recently developed. They all contribute to a better understanding of planets and satellites physics.

During the period, there have been several major events which have effected the scope and interest of Commission 19. The most significant of these has been the dissolution of the BIH and IPMS and their replacement by the International Earth Rotation Service (IERS). The correlation of higher frequency fluctuations in the Earth’s rotation rate with changes in the Earth’s Atmospheric Angular Momentum is also significant. Many investigators now seem to believe that the “decade variations„ in the Earth’s rotation rate are caused by torques between the core and mantle caused by the uneven motions at the core-mantle boundary. These events and discoveries have made this an exciting period. It seems that the future holds more in the way of discovery due to the utilization of the more accurate and precise Earth rotation data coming from the modern observing techniques.

In the past triennium members of the Commission 20 have been very active in studying positions and motions of minor planets, comets and satellites including rings by observational and theoretical investigations, as it is described in this report In fact observers have been producing tremendous amount of astrometric data, much more than we could imagine twenty years ago, when we heard many complains and appeals to observers for needs of more observations, particularly, for minor planets and satellites. Technically, several new devices to detect faint objects and to measure their positions more effectively, have been developed. Theoreticians have faced many interesting and important problems to explain observational facts with several powerful methods developed recently.

The different components of the light of the night sky have their origin in different formations of matter in the universe - encompassing a huge scale of distances ranging from a few kilometers in the earth’s atmosphere to the most distant known galaxies and beyond. Correspondingly, the borderlines to other Commissions are not very well defined and thus material relevant to Commission 21 can also be found in the reports of other Commissions on the following topics: zodiacal light and zodiacal IR emission (Comm. 22, 44), integrated starlight (33, 25), diffuse galactic light (34), extragalactic background light (47), airglow and atmospheric scattered light (50), and space-borne observations of the LONS (44). From the Commission 21 point of view the connecting link between these various fields is the special techniques utilized in the surface photometric measurements and reductions of background radiations which extend over the entire sky. One crucial problem is the separation of the LONS into its several components. The approach for solving this task is to utilize the different spatial distributions and different broad and narrow band spectral properties of each of the LONS component. Thus the successful measurement and separation of one of the LONS components requires a knowledge of the properties of all the other components. This situation has become apparent in recent years as the infrared background radiation database, provided by the Infrared Astronomical Satellite (IRAS), has been analyzed: both the zodiacal and galactic dust emissions have to be analyzed hand in hand, and both these components must be very accurately mastered before any conclusions are possible on the extragalactic component. It is also obvious that very similar problems are encountered in the ultraviolet and infrared wavelength regions as in the more traditional optical domain. Thus the techniques developed in one of these wavelength domains are directly applicable in the others.

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.