The past triennium has seen an unprecidented increase in our knowledge and understanding of the solar system and, in particular, of the planets and satellites of the outer solar system. This epoch – 1 January 1979 to 31 December 1981 – has witnessed major spacecraft missions to Venus, Jupiter and Saturn by the United States and the launch of further missions to Venus by the Soviet Union.

An avalanche of discoveries pertaining to the satellite and ring systems of Jupiter and Saturn followed from the encounters of Pioneer 11 with Saturn, of Voyagers 1 and 2 with both Jupiter and Saturn, and from the passage of the Earth through the Saturn ring plane, all of which occurred during the triennium. The first comet discovery from a spacecraft also occurred during the same interval, a coronagraph experiment on the satellite P78-1 apparently catching a Kreutz sungrazer in the last hours before it impacted the Sun on 1979 August 30. Several successfully observed occultations of stars by the Uranian ring system, by minor planets, and possibly by satellites of Neptune and Pluto testify to efforts inspired by the Commission’s Working Group on Prediction of Occultations.

The light of the night sky includes several components which spread all over the celestial sphere. These light components are terrestrial (airglow), interplanetary (zodiacal light), galactic (integrated starlight, diffuse galactic light) and extragalactic (extragalactic background light). Thus the study of nature of each light source, covering large distance, is pursued in different fields of astronomy. However, the techniques of measurement for respective components are similar and the knowledge of other lights is indispensable even in the study of a particular component.

Following past practice, a number of authors have contributed reviews of their own field. These contributions have been edited by the President to reduce major overlaps and in some cases, due to space constraints, to reduce the length of the reviews. When possible reference numbers in the Astronomy and Astrophysics Abstracts are used. As editor, the President accepts responsibility for any shortcomings in the report.

The name of this commission was recently changed from “Parallaxes and Proper Motions”. These data are at this time indeed obtained mostly by the techniques of photographic astrometry, but so is the bulk of relative star positions. It is clear, however, that the nonabsolute determination of relative positions and data derived from them in narrow fields (which describes the scope of this Commission) is going to be carried out more and more also by nonphotographic methods, namely photoelectrically (Earth and satellite based) by interferometry (optical, radio, and speckle) and by direct imaging. This therefore creates considerable overlap with the subject areas and methods of a number of other Commissions, especially Commission 8, and it will be appropriate for Commission 24 in the near future to examine critically the overlapping areas of interest and to come to an agreement about the definition of the proper responsibilities of the individual commissions.

Most astronomical observers at some time become involved in photometric techniques even if the participation may be limited to a rough check of the brightness of an object for measurement at the telescope. The field is in fact so broad that much of the current work is more appropriate to the reviews of other IAU Commissions and it has become accepted that Commission 25 deals mainly with those subjects which are of common practical interest to photometrists and polarimetrists around the world. We are now at the beginning of a new stage, that of observation with space telescopes and it will be important to ensure that the transition to the new techniques of measurement is a smooth one. In our review, we restrict our discussion to stellar work, leaving to other Commissions the consideration of photometry and polarimetry of stellar systems, solar system objects and gaseous nebulae. We consider recent work concerning detectors, photometric and polarimetric systems, standard stars and sequences, catalogues of new material and related items of interest to observers. The reference numbering system of Astronomy and Astrophysics Abstracts is used where possible. We shall draw attention to some important conference volumes and to some major observing projects completed during the last 3 years and finally shall look briefly towards probable developments and future prospects for the times ahead.

Since the summer of 1979, more than 17 000 visual measures were made and have either been published or are being prepared for publication.

Couteau, using the 50- and 76-cm telescopes at Nice, obtained 984 measures and also discovered 207 pairs. Of these, 13% are closer than 0″.25, and 33% have separations smaller than 0″.5. Also at Nice, Morel made 300 measures with the 76-cm refractor and discovered 6 pairs.

With the enormous rise in publication costs, the space available for these triennial reports is becoming ever more precious, while the amount of research to be reported on becomes ever larger. Thus while my predecessors have used this introductory section to detail the symposia and colloquia held over the past three years, as well as other administrative matters, I have decided to omit this material (which is available elsewhere) in favour of maximizing the space available for science reporting.

The present report covers the period 1979-1981. As with previous reports it has not been possible to write an all-inclusive account covering everything published, or even every field under investigation; the number of contributions to extragalactic research is increasing faster every year. Summaries of the papers may be found in the Astronomy and Astrophysics Abstracts.

During the interval covered by this report, Commission 29 has sponsored or cosponsored the following IAU meetings: Symposium 98 on “Be Stars,” Munich, FRG, April 1981; Colloquium 59, “Effects of Mass-Loss on Stellar Evolution,” Trieste, Italy, September 1980; and Colloquim 70, “The Nature of Symbiotic Stars,” Haute-Provence, France, August 1981. In addition, Commission 29, through its Working Group on Ap Stars, collaborated in the organization of the 23rd Liege International Astrophysical Symposium on Upper Main-Sequence Chemically Peculiar Stars. Several IAU symposia and colloquia proposed for 1982 and 1983 are also cosponsored by Commission 29.

This report reviews briefly the works achieved or planned in the triennium from 1979 to 1981 on the subjects to be considered by Commission 31. Reports of contributions furnished kindly from different institutions by many of Commission members were obliged to be partly omitted or abbreviated owing to the limitation of space, for which hearty thanks and apologies as well are to be given.

Astronomical observations for UTO-UTC have been continued on a routine basis in participating observatories to BIH with PZT's, astrolabes, transit instruments etc. The observations with 35-km interferometer have been made by USNO, and are expected to contribute an important part to future efforts.

According to Commission 33 traditions, the report contains contributions from a number of authors: K2 , D.L. Crawford, §3, W.B. Burton and F.J. Kerr, §4, W.B. Burton, §5, K. Loden, §6 A and C, R. Wielen, f-6 B, U. Haud and J. Einasto, §6 D and §7, D. Lynden-Bel], §6 E and F, M. Fujimoto.

The subject of interstellar matter continues to be one of the most active fields of present day astronomical research. The advent of new instruments operating in the different parts of the electromagnetic spectrum has resulted in a phenomenal increase both in the amount of observational material, and in the theoretical work attempting to interpret or model the observations. This has made it increasingly difficult to cite all of the published work in the field, and to have room to report even in brief on the conclusions of these studies.

Once again this report consists of detailed discussions of a limited number of topics of current interest, which have not been discussed in recent reports. The subjects are: Mixing in Stellar Evolution (A. Maeder); Supernovae (J. Craig Wheeler); Theory of Variable Stars (J. Cox); Theoretical Studies of Star Formation (J. J. Monaghan); The Age and Helium Content of Globular Clusters (V. Castellani). Because the first three contributions have been written by different authors there is a small amount of overlap in their contents. I am very grateful to the authors for providing their reports very promptly. The references are in general identified by their number in Astronomy and Astrophysics Abstracts but many references are too recent for this to be possible and a few others were not included in A & A Abstracts.

Commission 36 acts as a cosponsor of the following Symposia: (1) IAU Symposium No. 102 “Solar and Stellar Magnetic Fields: Origin and Coronal Effects” Zurich, Switzerland (2-6 August 1982) and (2) IAU Symposium No. 103 “Planetary Nebulae” London, UK (10-1U August 1982). The commission participates jointly with Commissions 29, 35, and 45 in the organization of a Joint Discussion at the IXth General Assembly on the topic “Mass-Loss-Phenomena”.

The past triennium has been a very active period in most branches of cluster research. Some controversial subjects, notably globular cluster abundances and ages have received much attention. A good number of photometric papers on clusters as well as associations have been published. Observational effects of mass loss have been discussed by several astronomers.

This report has been assembled by the president of the commission although several sections have been contributed by other members. The report will first list some highlights in the activities of our commission. Then follow the tables containing current investigations of OB associations, open clusters and globular clusters. These have been assembled by B. Balázs, G. Harris and R. White, respectively. After these tables comes a section by D. Heggie about dynamics of star clusters. A working group under the chairmanship of A. Moffat has made a proposal about the numbering of stars in clusters. The proposal, which is included here will be discussed by our commission at the IAU General Assembly.

This report covers surveys of radio sources, basic measurements of source parameters and new developments in radio telescopes, instrumental techniques and data processing. The period covered is approximately late 1978 to about August 1981. The results and conclusions of astronomical investigations based on measurements made through the radio window are included in the reports of other commissions, as relevant. Following the practice adopted in 1979, a circular was sent to the Presidents of 18 IAU Commissions and to all members of Commission 40 describing the proposed format of the present report and also identifying contact persons who could be consulted to avoid duplication and to ensure that radio astronomical results are adequately covered by various commissions. I am grateful to all concerned for providing the necessary coordination.