An important topic of current interest both in solar and stellar physics is the possibility of identifying solar phenomena in stars through an understanding of these on a global scale on the sun. We concentrate here on the recent research concerning the variability in solar irradiance from disc integrated observations (sun as a star) in the white light as well as in monochromatic wavelengths.

As the pool of fundamental data available to astronomers continues to increase, the question of how best to promote the necessary cross-discipline interaction becomes increasingly important. Commission 14 has traditionally played an important role in this activity, by publishing triennial reports in the IAU Proceedings, as well as by responding to more specific requests for data. We are fortunate in having the support for these activities of some energetic Working-Groups and Chairmen, whos contributions to the present report are very gratefully acknowledged. With the expansion of available data it is appropriate that these reports take on more and more the form of references to review articles and other more specific data bases. The question of whether the field of activity of the Commission should be enlarged was discussed at Patras and will be reviewed again at the Delhi meeting. One possibility is to include nuclear processes and fundamental particle physics. On the other hand a rationale for limiting the scope of our activities might be the direct application to astronomical observations. Astronomical theorists are usually better placed to access the fundamental data themselves. The interaction between fundamental physics and astronomy will in general take two forms. There is the essential service role of making data available in a usable form. However, we should surely aim to stimulate the other very profitable mode, in which the two disciplines are brought together to form real scientific collaborations, in order to research the problems of astronomy.

The proceedings of the 6th and 7th International Conference on Spectral Line Shapes shown the general state of advances of the subject. Though a great part of the actual content lies outside the present interest, a number of useful results for astrophysical purposes can be found therein and will be quoted hereafter.

Because of the magnitude and diversity of material on electron and heavy-particle collisions, I gave references only to published papers of obvious immediate relevance to astronomical research.

A Bibliography on Atomic Energy Levels and Spectra covering the period July 1979 through December 1983 is scheduled for publication in late 1984(1). The references in Table 1 are thus limited to papers published or known to be in press in 1984; the selection was made from references giving data on energy levels, wavelengths, and line classifications for spectra of the elements Z < 30. S. Johansson notes that the spectra under investigation in the Physics Department of Lund University, Sweden, include S III, IV, VII, VIII, IX; CI VI, VII, VIII, X; Sc V; the (Ne I) isoelectronic spectra Sc XII-Fe XVII; Ti I; Cr I, II, V; Fe II, III; and several high-ionization spectra of Ni, the work on Fe III and the Ni spectra being done in collaboration with researchers in the Zeeman Laboratory, Amsterdam. Term analyses in progress at the Lund Institute of Technology, as reported by W. Persson, include Ne III and K II, III. This group has recently completed analyses for Kr IV, Rb V, Sr V, VI and has papers in preparation for Rb IV, Y VI, and Xe II. Fourier-transform spectrometric observations at the National Solar Observatory (Kitt Peak) by J. Brault and collaborators are yielding more accurate and complete line lists for the first and second spectra of several elements, including Mg, Al, Ti, V, Cr, Fe, and Ni. Ongoing extensions of the term analyses for some of these spectra were mentioned above; similar work is underway for Mg I, II, Al I, II, and V I, II (E. Biemont, University of Liege) and for Fe I (R. C. M. Learner, Imperial College, London). B. C. Fawcett’s current research at the Rutherford Appleton Laboratory, Oxfordshire, England, includes work on the oxygen-like spectra P VIII through Fe XIX.

Research in molecular spectroscopy over much of the electromagnetic spectrum has continued intensively over the past three years. It has been stimulated not only by the imperatives of fundamental research programmes in many laboratories, but also by the impact of molecular lasers on the field, and the needs of atmospheric and environmental programmes. The literature is so prolific that it is impossible even to review briefly here all that is relevant to astrophysical needs. Thus most of this report has been compiled from the contributions from individual workers and Research Centres.

The last three years have witnessed a growing interest in the physical properties of the small bodies in the solar system. Perhaps the most significant impetus to research on small bodies has been the imminent arrival of Comet Halley in the inner solar system. This famous comet, which was recovered in autumn 1982, has been the object of intense study during the past year as it has approached the sun and developed a tail. Much of the international, ground-based astronomical research on Halley has been coordinated through the International Halley Watch program. Spacecraft from several nations have been successfully launched (or soon will be, we hope) and are on their way to intercept the comet and make close-up observations and in situ measurements. The commencement of spacecraft study of small bodies marks a new era in comet/asteroid science and, in coordination with ground-based and Earth-orbital observations, will result in unprecedented new knowledge about the origin of the solar system and about solar system processes. Although Halley is receiving the most attention, interest is also high in Comet Giacobini-Zinner, the vicinity of which will be probed by a diverted American spacecraft in September 1985. Upcoming spacecraft studies of comets through 1986 are described at the end of the comet section of this report. Asteroid exploration by spacecraft is also anticipated to begin in the near future. The trajectory of the NASA Gailieo Mission to Jupiter has been changed to permit close-encounter observations of the large main-belt asteroid 29 Amphitrite in December 1986; these observations will be conducted on a “best effort” basis only a few months after launch of Galileo. Interest is also high in Europe, the Soviet Union, and the United States in possible spacecraft missions to additional comets and asteroids during the 1990’s. If these efforts are pursued, there will be a concomitant ground-based effort. The last three years have also witnessed extremely productive efforts to observe small bodies from Earth orbit. For example, the Infrared Astronomical Satellite discovered a comet in 1983, which made the closest approach to the Earth of any comet in centuries. IRAS made important discoveries and measurements of other comets and also assembled an immense database on infrared brightnesses of thousands of numbered and unnumbered asteroids. The planned launch of the Hubble Space Telescope next year highlights the continuing potential for applying extremely powerful instrumental techniques to the study of comets and asteroids from above the Earth’s atmosphere.

During past three years from 1982 to 1984 we saw the further progress in the planets and satellites research by the space and ground-based technique, in the analysis and interpretation of the observational data. Inspite of some decrease of the activity in the planetary spacecrafts launches during this period (except of two Soviet missions to Venus) many important scientific results were obtained from the continued reduction and analysis of the measurements which were performed by Mariner 10 (Mercury), Pioneer Venus, Venera 13 and 14, Viking (Mars), Pioneer 10 and 11, and Voyager 1 and 2.

During the period, work on the problem of the Earth’s rotation has continued to expand and increase its scope. The total number of institutions engaged in the determination of the Earth’s rotation parameters (ERP) by different techniques has been increased significantly. The rotation of the Earth is currently measured by classical astrometry, Doppler and laser satellite tracking, laser ranging of the Moon, and radio interferometry. Several long time series of the ERP are available from most of these techniques, in particular, those made during the Main Campaign of the MERIT project. The various series have been intercompared and their stability, in the time frame of years to days, has been estimated for the purposes of establishing a new conventional terrestrial reference system (COTES). On the other hand, the difficulties of maintaining a regular operation for laser ranging to the Moon (LLR) have been recognized. It resulted in the proposal to organize an one-month campaign of observations in 1985 in order to complement the COTES collocation program and to allow additional intercomparisons with other techniques.

Interest in minor planets and comets continued to grow during the triennium, sparked in part by the highly successful 1983 mission of the Infrared Astronomy Satellite (IRAS) as well as by activities associated with the return of P/Halley and the first spacecraft missions to comets. A trial of the Astrometry Network of the International Halley Watch (IHW) on P/Crommelin was quite successful. Yet with an increasing need for precise ephemerides, there continued to be concern for acquisition and timely reporting of astrometric observations of even the best known comets.

The light of the night sky consists of atmospheric components (airglow, light scattered in the atmosphere) and – even in the case of spaceborne observations – of zodiacal, galactic and extragalactic light. Although all components are of similar importance, investigations on zodiacal light have profitted most by the space age since their object of research, the interplanetary dust cloud, became accessible to direct in-situ measurements. Lunar samples and measurements by micrometeoroid detectors provide individual and eventually detailed information on impact events, which however are limited in number and therefore restricted in statistical significance. Zodiacal light investigations involve scattered light of many particles in large volume elements and therefore provide global information about physical properties and spatial distribution of interplanetary dust grains, however just in terms of average values. Therefore both sources of information are complementary and a synthesis can only be achieved by synoptic interpretation of zodiacal light, micrometeoroid, and meteoroid investigations also including dynamical aspects. Measurements of zodiacal light (and emission) from rockets, manned or non manned spacecraft, and deep space probes gained drastically in importance compared to ground based observations. On the other hand investigations on airglow have become more and more a topic of geophysics Caeronomy). They remain relevant however to astronomy as far as photometric features are concerned. These general trends continued in the last triennium and have influenced the activities of our commission.

Following past practice, a number of authors have contributed reviews of their own field. The contributions have been edited by the President in order to avoid some overlaps, to reduce the length of the reviews an to add some publications. When possible reference numbers in the Astronomy and Astrophysics Abstracts are used. As editor, the President accepts responsibility for any shortcamings in the report.

The question of the title of Commission 24, obviously, offers a difficult problem as already mentioned in recent reports. Photographic Astrometry no longer describes the whole scope of the commission. This problem has continued during the last three years especially in view of the preparations for the astrometric tasks of the NASA Space Telescope and of the ESA satellite HIPPARCOS.

This triennium has in general not been one of spectacular new developments in photometric of polarimetric techniques; rather, existing techniques have been improved and are being exploited by more observatories than before. For this reason, the previous report (31.113.097) should be consulted for a broad survey of the subject, while the present has the character of a progress report.

There is little doubt that array detectors of some kind will eventually take over from the single-pixel detectors now used for precise work. The takeover, however, is a gradual process; more and more problems are encountered as the required precision is raised. Very broadly speaking, the best array detector practice has now reached 0.01 mag in photometry and 0.1% in polarimetry (0.001 and 0.005% respectively for single detectors). Whenever this precision of the array detectors is sufficient and the multiplex advantage vital to the programme comtemplated, the array detectors are the indicated path to progress (see, for instance, Ref. 1).

Commission 26 has changed its name. The new denomination, warmly promoted by Dommanget, represents more adequately the actual field of the Commission Itself and appears as a good start for extending its interest beyond the traditional aspects (morphology and statistics) and plunging into problems connected with the origin, evolution, mass spectrum and dynamics of small star associations.

The field of variable-star research is so broad that no report of this nature could possibly mention all the papers that have appeared in the last three years. It is hoped, however, that the reviews below include the most important work and identify the most significant trends. This report comprises ten sections on as many different research topics, each written by a different member of Commission 27. In addition there are (in Section 12) three short reports about ongoing activities of the commission. The commission president is very grateful to the authors of the individual contributions who have worked so conscientously.

The present Report covers the period 1982-1984. As with previous Reports, it has not been possible to cover all publications or even every field of research. Some subsections of this Report, the Magellanic Clouds for example, report a body of work as extensive as that in some commissions.

During the triennium under review, Commission 29 has sponsored or cosponsored the following IAU meetings: Symposium 102, “Solar and Stellar Magnetic Fields,” Zurich, Switzerland, August 1982; Symposium 108, “Structure and Evolution of the Magellanic Clouds,” Tübingen, FRG, September 1983; Symposium 111, “Calibration of Fundamental Stellar Quantities,” Como, Italy, May 1984; and Colloquium 82, “Cepheids: Observation and Theory,” Toronto, Canada, May-June 1984. Commission 29 has also supported or sponsored several IAU meetings proposed for 1985 and 1986. They include “Luminous Stars and Associations in Galaxies,” Porto Heli, Greece, May 1985; “Upper Main Sequence Stars with Anomalous Abundances,” Crimea, USSR, May 1985; “Astrochemistry,” Goa, India, December 1985; “Hydrogen Deficient Stars and Related Objects,” Bangalore, India, December 1985; “Circumstellar Matter,” Heidelberg, FRG, June 1986; and “Be Stars,” Boulder, USA, August 1986.

This report covers the period June 1981 to June 1984. and includes some material from IAU Colloquium No. 88, October, 1984.). The field of radial velocities has undergone a renaissance in the last few years as the new radial velocity machines have come into use. Not only can stars of much fainter magnitudes be reached, but the precision of the measured radial velocity has been increased by orders of magnitude. Instead of speaking of velocities accurate to kilometers per second it is now possible to measure velocities to tens of meters per second. Research programs, involving these new techniques are now underway involving the study of hundreds, and in some cases, thousands of faint stars.