The partition of the subject matter of this report follows that of earlier reports. Drafts for individual sections or parts of such were contributed by C. Arpigny, L. Biermann, A. H. Delsemme, O. V. Dobrovolsky, L. Haser, G. Herzberg, B. J. Levin, Rh. Lüst, E. Roemer, V. Vanýsek, and K. Wurm. The overall editing was done by Mrs Rh. Lüst, V. Vanýsek, and the undersigned.

Before mentioning some of the more important developments it is noted that E. Roemer has continued to publish every few months short notes on comets in the Publications of the A.S.P. The annual reports in Quarterly Journal of the Royal Astronomical Society have been continued by B. G. Marsden and J. G. Porter.

Several collections of Russian papers have been published which give a survey of the work done in the U.S.S.R. The description of physical characteristics of comets which appeared from 1961— 1965 was continued by S. K. Vsehsvjatskij, who also completed a book on Nature and Origin of Comets and Meteoritic Matter.

The ground-based research activity in the planetary field has increased very rapidly since the Prague meeting in 1967. The space probes into the atmosphere of Venus and the flybys of Mars have not only added directly to our knowledge of these planets but have stimulated further research.

Because of this rapid growth and the large expense which would be required to publish detailed descriptions of the very numerous research projects carried on in the last three years, this report will differ in important respects from the previous ones. Drs Levin, Pettengill, and McElroy have provided summaries of progress made in three important fields of planetary science, and Levin has also kindly contributed a summary of planetary research carried on in the U.S.S.R. since the Prague meeting. On behalf of its members, the President of Commission 16 gratefully acknowledges each of these important contributions.

Selon les instructions reçues de la part du Secrétaire Général de l’UAI, l’esprit général du présent “Draft Report” de la Commission 17 “La Lune” ne doit plus représenter, comme par le passé, un résumé des travaux effectués dans la discipline au cours des trois dernières années. Son rôle sera de donner un aperçu général sur les aspects et les tendances des recherches sur la Lune, la contribution présente et future de la Commission 17 du l’UAI dans son développement, ainsi que les coopérations dont elle est l’objet ou devrait l’être dans l’avenir.

La commission déplore le décès de Madame Aksentieva, directeur de l’Observatoire de Poltava et du Professeur Demetrescu, ancien directeur de l’Observatoire de Bucarest.

L’étude de la rotation de la Terre poursuit plusieurs objectifs scientifiques fondamentaux:

1. (1) Fournir des données d’observations continues d’où l’on pourra tirer un ensemble de paramètres servant de base à l’élaboration des théories sur la constitution interne de la Terre et sur la dynamique du système Terre-Lune.

2. (2) Fournir à tout moment la position d’un trièdre de référence attaché au manteau terrestre par rapport à un trièdre fixé dans l’espace, travail d’une nécessité primordiale pour l’astronomie fondamentale, la géodésie et la navigation spatiale.

3. (3) Permettre de nouvelles recherches sur certaines constantes fondamentales de l’astronomie (nutation, aberration) grâce à la constitution de très longues séries d’observations homogènes.

The Report in the part dealing with the minor planets and satellites has been compiled at the Institute of Theoretical Astronomy in collaboration of S. G. Makover (minor planets) and V. A. Shor (satellites). Contributions to this report have been received from S. Arend, H. Debehogne, J. Dommanget, P. Herget, S. Herrick, G. M. Jannini, B. G. Marsden, V. V. Michkovitch, B. Milet, Z. M. Pereyra, B. Popovič, E. Rabe, E. Roemer, J. Schubart, W. Strobel, C. Torres, H. Wood. The part on comets has been prepared by E. Roemer.

The main feature of minor planet research during this triennium has been the further application of modern electronic computing machines to the practice of computing. The time has gone when the computations of orbits and ephemerides were performed with the aid of logarithmic tables or with desk calculators. Therefore it is no wonder that all computational work in the field of the motion of minor planets is nowadays concentrated in a limited number of institutions provided with powerful up-to-date computing techniques, like the following.

1. (1) Institute of Theoretical Astronomy, Leningrad has used till recently a computer BESM-2 and now has at its disposal a new more powerful computer BESM-4.

2. (2) The Observatory of Cincinnati has used till recently a powerful computer NORC. Unfortunately this machine has been nowadays dismantled, but the observatory can perform some kinds of computations with an IBM-360 computer.

3. (3) Latvian State University, Riga, has made a large amount of computations with the computer BESM-2.

4. (4) University of California, Los Angeles, makes a large amount of computations with its own computer.

Studies of airglow, zodiacal light, and galactic light in this triennium were almost as active as in the last. Results of observations obtained during and after the IQSY were the major contributions in this term. Night Airglow studies during the IQSY were widely reviewed in the Annals of the IQSY, vol. 4, in which the following articles are included:

“Night Airglow Observations during the IQSY” (F. E. Roach, L. L. Smith and J. R. McKennan);

“Airglow Research during and since the IQSY” (G. Weill);

“Hydrogen and Hydroxyl Emissions in the Nightglow” (N. N. Shefov and Yu. L. Truttse).

Proceedings of the NATO Advanced Study Institute, July 29-August 9,1968, entitled Atmospheric Emissions, contains some ten significant papers on airglow both in observations and interpretations. Many of them are referred to in the following sections.

Many stations have been engaged in airglow observations since the beginning of the IASY in 1969, although the number of stations seems to be a little less than during the IGY. Stations near the equator and in the southern hemisphere, however, are more numerous and active than during the IGY in response to the strong wishes of many airglow researchers. These efforts are being made especially by G. Weill’s group of France, V. J. Dachs’ and Lange-Hesse’s groups of Germany.

The limited space made available for this report by recent regulations of the Executive Committee of our Union does not allow the traditional list of all published papers. Also, it omits the data on detection of cosmic dust, which are now published each year in surveys by the COSPAR Dust Panel. This report is mainly based on completely fresh information contained in numerous letters sent to me.

The accompanying report of our Meteorite Committee is done in the old style, but only a limited number of references are given. Evidence for a terrestrial origin of tektites is becoming stronger every year, and this subject is omitted in order to shorten the report.

Before starting the report, I mention with great regret the death of Prof. Dr Cuno Hoffmeister. His name remains connected forever with the famous period of naked-eye observations of meteors. Another great loss for meteor observers was the death of Mr Koiro Komaki, the President of the Nippon Meteor Society.

Several monographs and collections of papers were published in Meteoritics during 1967 to 1969 (Chirvinskij, 1967; Vdovykin, 1967; Wood, 1968; Cikulin, 1969; Anders et al, 1967; Stanjukovič, 1968). Extensive work on meteorites is continuing in the Meteorite Committee of the Academy of Sciences of U.S.S.R. Fesenkov and Krinov continued publishing the journal Meteoritika, where most of the papers of scientists of the U.S.S.R. are published. Hoffleit continued publishing Meteoritics of the Meteorite Society. Javnel’ continued editing a bibliography on meteorites. A bibliography on the isotopic and chemical composition of meteorites was published by Kielbasinski and Wanat. The UNESCO working group on meteorites under the chairmanship of Orcel edited the Directory of Meteorite Collections and Meteorite Research in 1968.

The Meteorite Committee of the Academy of Sciences of the U.S.S.R. organized its 13th meteorite conference in 1968. The Meteorite Society had its 30th to 32nd annual meetings during 1967 to 1969. The International Atomic Agency in cooperation with UNESCO and five other international scientific unions and organizations including the IAU represented by Millman, prepared a Symposium on Meteorite Research in Vienna, Austria, 7-13 August, 1968, initiated by the UNESCO Working Group on Meteorites. More than 70 papers were presented at this Symposium, showing the interests of various sciences in meteorites. The Symposium volume appeared very soon after the sessions were closed in the series Astrophysics and Space Science Library, published by D. Reidel Publishing Company, Dordrecht, Holland, under the title Meteorite Research edited by P. M. Millman (1969, 940 pages).

There seems to be a consensus of opinion that the useful life of the commission has come to an end with the achievement of the principal aim of the historical task of the Carte du Ciel, presenting an overall picture of the Heavens as to positions of the fixed stars up to a definite limiting magnitude. The French presidents in succession with great energy, supported by the IAU, succeeded in overcoming all obstacles and in finishing the printed Astrographic Catalogue. Remaining tasks of deriving definitive plate constants, eventually deriving reliable proper motions of all stars in the programme evidently rests with individual observatories or at other commissions of the Union within their proper frame of activities.

Following a suggestion presented at the meeting of the Executive Committee in September 1969 a decision was reached to abolish the Commission 23 proper by merging it with Commission 24 (Stellar parallax and proper motion), and a working group in the latter commission would become a suitable means to continue work on data furnished by the Astrographic Catalogue.

Several of those observatories still in possession of Carte du Ciel-astrographs are going on with proper motion (p.m.) work in their zones or are preparing to do so. The application of the astrographs to the programme of attachment of stars to galaxies according to A. N. Dejč’s method is in progress.

At the Pulkovo Observatory a parallax programme has been started by Kanayev for 120 stars chosen mainly from Vyssotsky’s lists and the Leningrad list of multiple systems. Proper Motions relative to galaxies have been determined by Fatchikhin for 14669 stars in 85 different fields; the magnitude equation is being investigated and secular parallaxes as well as the solar apex and the constants of galactic rotation are being calculated. The general programme on absolute proper motions is being carried out by Dejč at Pulkovo, and at Cerro Calan in Chile, by Panteleyeva at Sternberg, and by Rahimov at Tashkent.