This Report is compiled by using the reports of the Directors of the national ephemeris offices reviewing the programs for the preparation and publication of astronomical ephemerides of variuos purposes, i.e. for astronomers and space scientists, marine and air navigators, and surveyors. Some proposals of Commission members are also included. The Report may be of interest also to other I.A.U. Commissions, and mainly to Commissions 7, 8 and 31. Principal topics belonging to the Commission competence and some items to be presented to the XVIIth General Assembly of the I.A.U. in Montreal will be reviewed in following comments.

A la requîte de J. Sahade, Président du POGSI, les membres de la Commission 5 ont donné des avis sur ce problème. Quelques extraits significatifs des suggestions relatives aux solutions possibles:

As noted below in the report of the Central Bureau, a number of changes have been introduced in the technical and business operations of the Bureau during the triennium. Some of the changes follow from the transfer of the IAU Minor Planet Center to the Smithsonian Astrophysical Observatory. For example the Minor Planet Circulars now offer an alternate avenue of publication for less time-urgent data concerning comets as well as minor planets. Changes at the communications center of the Smithsonian Astrophysical Observatory have made it less costly, as well as more efficient, for the Central Bureau to maintain its own communications equipment. At the same time, in the face of generally rising costs, and after careful investigation of alternatives, it has become necessary for users to assume an increased share in underwriting the operating expenses of the Bureau.

This report is organized according to twelve subjects of interest in modern celestial mechanics. Emphasis is placed on the results of an exhaustive literature search in which assistance was received from several members of Commission 7. The impetus on celestial mechanics by space projects, by new observational techniques and by the use of high speed electronic computers continued to be of considerable importance. The fact that celestial mechanics became an experimental science is still too recent to be fully evaluated. The high accuracy of radar and laser observations, the new analytical and numerical techniques, the recent sophisticated statistical orbit determination methods and many other results achieved during the past three years suggest that celestial mechanics is an exploding field of science in which new and exciting results emerge. Celestial mechanics is influencing other fields of scientific endeavor and is intimately connected and embedded in almost all areas of modern astronomy and space research.

It is clearly impossible to prepare a comprehensive review of three years’ work in the field of astronomical instrumentation within the space available in this volume. The selection of topics included and the space devoted to each is therefore largely subjective; some emphasis has been placed on material unlikely to be generally available elsewnere.

The title of our Commission was last changed in 1964 from “Commission des Etalons de Longueur d’Onde et des Tables de Spectres” to the present title recognizing the broader scope of the Commission. This was initiated by new observing techniques and refined theoretical models. In 1966 it was decided to add two more objects to the work of the Commission: Broadening of spectral lines and collision cross sections. The present structure of the Commission dates back to 1970. Since then the work of the Commission is not well described by the name “Fundamental Spectroscopic Data”. This is a hindrance in the recruitment of new members, especially those who represent new fields of interest. But the answers to an enquiry about change of name were so divergent within our Commission that so far no action was taken.

The Data Center on Atomic Transition Probabilities at the National Bureau of Standards, Washington, D.C., has continued its bibliographical and critical compilation work on transition probabilities. A new general bibliography has been published, covering the literature references through October 1977 (1).

Stark broadening (1) and polarisation shift effect in high density plasmas (2) have been reviewed. Critical reviews and a tabulation of selected data of the Stark widths and shifts of lines of non hydrogenic atoms and ions have been published (32,33).

The ongoing program of the Atomic Energy Levels Data Center (National Bureau of Standards) to produce new compilations of critically evaluated energy level data is at present focused on the first thirty elements. The most recently completed compilations in this series give energy levels for all the spectra of Mn (Mn I-XXV) (1), Cr (Cr I-XXIV) (2), V (V I-XXIII) (3), Ti (Ti I-XXII) (4),Ca (Ca I-XX) (5), and Al (Al I-XIII) (6), and work is underway on the spectra of K and Mg. C.E. Moore’s “Selected Tables of Atomic Spectra” now include 0 1 (7), 0 VI, O VII, and O VIII (8), work on the tables for the remaining oxygen spectra is in progress. A finding list for lines of the multiplets in Sections 1-7 of Moore’s NSRDS-NBS 3 series has been compiled by Adelman et al. (9). A recent publication of the AEL Data Center, “Atomic Energy Levels - The Rare-Earth Elements” (10), gives energy-level data for 66 spectra of the 15 elements La through Lu (Z=57-71), including a number of astronomically important spectra. A review of rare-earth spectral data by Blaise et al. (11) gives partial tables of energy levels and wavelengths and includes data on hyperfine-structure and isotope shifts. The first version of a much needed new compilation of “Line Spectra of the Elements” has recently been published (12). These tables contain some 42,000 lines, including the stronger lines of the first and second spectra of 98 elements and lines of the third, fourth, and fifth spectra for about half the elements from the vacuum ultraviolet to the far infrared. Outred (13) has compiled 8885 selected lines of 57 elements in the infrared region 1-4 pm, with energy-level classifications being given where available. Energy-level and Grotrian diagrams for the atoms and positive ions of the elements H through P (Z=l-15) have been prepared by Bashkin and Stoner (14), and further publications for the heavier elements are planned. The AEL Data Center (NBS) expects to publish in 1979 a “Bibliography on Atomic Energy Levels and Spectra” for the period July 1975 through December 1978 (15). Edlen’s 1976 review of term analysis of atomic spectra has references for spectra of the elements He through Ni (16), and Adelman et al. (17) have compiled an astronomically oriented bibliography on atomic autoionization. A bibliography on experimental isotope shifts in atomic spectra by Heilig (18) gives 666 references.

Molecular spectroscopic activity, and its literature, has continued to proliferate strongly during the reporting period. There has been much work over the entire wavelength range: microwave - extreme ultraviolet. The impact of the methods of laser spectroscopy on the field, and developments in molecular lasers have continued to provide a great stimulus to molecular spectroscopic research. There has also been increasing recognition of the need for fundamental spectroscopic data of all kinds in astrophysical, atmospheric and enviromental research applications. The scope of contemporary interests is displayed in the programme books for the symposia on Molecular Spectroscopy held annually at the Ohio State University. For the past three years the literature of the molecular spectroscopy has been so prolific that it is impossible to make a definitive review even of the astrophysically important contributions beyond brief citations. Important trends are indicated below. Literature citations have been principally compiled from the reports received from individual workers in Centres of Research on molecular spectra.

Comets, minor planets and meteorites provide us with valuable information about the past history of the solar system. They belong to the most primitive samples of the primordial solar nebula. Over the past years, we can record a considerable increase of interest in these bodies.

The explosive increase in the number of published papers on planetary and satellite research in recent years has made it impossible to provide an adequate summary of progress in the field over a given three year period in the space allotted for this purpose. The problem is particularly acute for the current epoch - 1 January 1976 to 31 December 1978 - because it encompasses major missions to Mars and Venus by the United States and the Soviet Union, as well as a large number of exciting discoveries made from the ground.

Members of Commissions 16 and 17 have voted by a substantial margin (102 yes, 4 no, 1 abstention) to merge the two Commissions. The merger will take effect at the 17th General Assembly.

The Astronomical Council of the Academy of Sciences of the U.S.S.R. Two statistical models of regolith dynamics were investigated in cooperation with the Institute of Geochemistry. The dependence of material distribution upon depth and time and the dependence of crater distribution upon radius and shape of craters were studied. The theoretical hypsographic curve was drawn for the relief stipulated by cratering. The evolution time of the layer was shown to be the product of two factors, the first one depending only on the initial depth of deposit of the layer and on the size distribution of craters, and the second one corresponding to the extent of processing of the layer, depending on the size distribution and shape of craters (G.A. Leikin et al., Astron. Vestnik, [2], 1978).

The commission deeply regrets the deaths of our colleagues which were reported in the several circular letters issued during the last three years.

The past triennium has been noteworthy for several significant discoveries in the outer part of the solar system. The discovery of the rings of Uranus was inspired by the activities of Commission 20’s new Working Group on Occultations. Although the discovery of a probable Plutonian satellite has not yet been completely confirmed, the implication that Pluto’s mass is only 0.002 earth masses may make it desirable to consider whether Pluto should be relegated to minor-planet status. The orbit of Pluto is in fact not greatly dissimilar to that of the object classified as the new minor planet (2060) Chiron, which was found to have its aphelion near the orbit of Uranus and its perihelion just inside the orbit of Saturn.

L’afflux des résultats, évidemment lié aux techniques spatiales, améne à définir ici de façon plus stricte le champ de la Commission, en continuant d’ailleurs dans la tendance du rapport précédent: le terme “Lumière du Ciel Nocturne” ne s’applique plus qu’aux émissions et diffusions, de l’UV à I’IR, qui recouvrent la sphère cèleste entière. De plus, parmi les composantes telluriques, ne sont prises en consideration que celles dont l’obtention correcte de composantes astronomiques exige la connaissance. Les interpretations sont maintenues, surtout quant aux propriètès optiques des poussieres interplanètaires et interstellaires, mais il n’est plus possible d’inclure, entre autres, les observations non-optiques des grains interplanétaires, leur étude dynamique, ou le rayonnement IR du centre galactique.

This report follows its predecessor in attempting to review significant developments in the field rather than constituting an extensive bibliography. As before, several sections have each been contributed by one author and the President has combined these editorially and attempted to ensure that all major areas have been adequately covered. Thanks are due to individual scientists who responded to requests for information from the authors of sections, to the authors of each section for the care with which they prepared the material, and to Dr. A.N. Simonenko for her help in preparing a summary of recent work in the U.S.S.R. which was of great value in editing the individual sections. As before, references from Astronomy and Astrophysics Abstracts have been used when available.

The scientific interest in Commission 31 topics and their applicability to new and practical fields is exponentially growing, pushing towards the recognition of new problems and subsequent research. In some cases as in Primary Standards the state of the art seems to be rather close to the actual and imagined needs. In other cases as in worldwide precise and accurate synchronization, we have to recognize that we still are far from the goals.

During the period 1 January 1976 to 31 December 1978 the Commission awarded grants to the following eighteen astronomers to enable them to visit institutions in other countries.