Proceedings from the Second Trieste Colloquium on Astrophysics, September 12-17, 1968

Nine years ago, in 1967, a conference on spallation nuclear reactions and their applications in astrophysics was held at the University of Pennsylvania. I Since that time, a number of devel opments have given renewed impetus to the study of spallation reactions. Among these are the successful acceleration of high energy heavy ions in the laboratory and their potential use in cancer radiotherapy, the availability of returned lunar rocks containing records of past cosmic-ray irradiation, and the devel opment of the theory that the spallation of interstellar matter is responsible for much of the observed universal abundances of the rare light nuclides. In May 1975, a new conference on spal lation nuclear reactions and their applications to astrophysics and radiotherapy was organized and held, again at the University of Pennsylvania. The papers in this volume are primarily expanded and updated versions of invited papers given at that conference. To the authors of the papers, we owe a debt of gratitude for their contributions and for their forbearance. The confer ence itself was much stimulated by the services of the four session chairmen: William A. Fowler, Serge A. Korff, Robert Serber, and Maurice M. Shapiro, each of whom has over the years made fundamental contributions to the subject matter of this volume. Crucial support for much of the editorial work was provided by the National Aeronautics and Space Administration and the National Science Foundation. George W."

This volume contains the detailed text of the lectures delivered at the International Workshop on Space Dynamics and e*elestial Mechanics held in Delhi, India during November 14-16,1985. This workshop was organised under the joint sponsorship of University of Delhi, Delhi, Vikram Sarabhai Space Centre, Trivandrum (India) and the Space Programme of the University of Texas at Austin, Austin, USA. The main objective of the workshop was to review the current state of the art in the area of Space .Dynamics and Celestial Mechanics thr- ough paper presentations, key note addresses, lectures and discussions, to expose the participants to more recent developments in varjous tech- niques, analytical as well as numerical, as applicable to Space Mecha- nics, to identify and assess the degree of augmentations desirable in respect of software packages available for this purpose with different centres and to establish contacts with experts in the vital field with a view to facilitate the in flow of technical inf~rmation. The whole material of this volume has been organized into seven basic areas: (i) The key note address by Professor V. Szebehely, (ii) General Celestial Mechanics, (~ii) Solar System and Natural Satellites, (iv) Stellar Systems and Galaxies, (v) Orbit Determination and Satellite Theory, (vi) Attitude Motion and (vii) Mission Planning and Control.

Two years ago, just before the Prague meeting of the International Astronomical Union, Armin Deutsch made the bold suggestion that the space spectroscopists hold a joint symposium with the ground-based observers. At that time the rocket observa- tions of stellar spectra seemed too meagre to make such a meeting worthwhile, but we proceeded in the hope that there would be significant new results available by 1969. IAU Commissions 29 and 44, on Stellar Spectra and Observations from Outside the Terrestrial Atmosphere respectively, agreed to sponsor the symposium so that the organization was given to the Joint Working Group of these commissions. Conse- quently, the Organizing Committee, which met first in Prague, consisted of A. Deutsch, M. W. Feast, L. Houziaux, V. G. Kurt, N. G. Roman, J. Sahade, A. B. Underhill, and R. Wilson, with myself as Chairman. Later COSP AR was invited to join in spon- soring the symposium and T. Chubb was added as their representative. We were specially pleased when C. de Jager invited us to the Netherlands and offered the services of the Utrecht Observatory for the local organization. He suggested we hold the meeting at the new Lunteren Conference Centre located in a wooded area some 35 km east of Utrecht. The modern facilities of the Centre and the hospi- tality of its staff contributed much to the enjoyment of our four days there.

IAU Symposium Number 52 on Interstellar Dust and Related Topics was held at Albany, N.Y., on the campus of the State University of New York at Albany from May 29 to June 2, 1972. The members of the Organizing Committee were: Dr A. D. Code, University of Wisconsin, Madison, Wis., U.S.A. Dr B. D. Donn, Goddard Space Flight Center, Greenbelt, Md., U.S.A. Dr A. Elvius, Stockholm Observatory, Saltsjobaden, Sweden. Dr T. Gehrels, Lunar and Planetary Laboratory, University of Arizona, Tucson, Ariz., U.S.A. Dr J. M. Greenberg (Chairman), State University of New York at Albany, Albany, N.Y., U.S.A. Dr H. C. van de Hulst, Sterrewacht, Leiden, Holland. Dr S. B. Pikel'ner, Sternberg Astronomical Institute, Moscow, U.S.S.R. Dr E. E. Sal peter, Cornell University, Ithaca, N.Y., U.S.A. Dr B. E. Turner, National Radio Astronomy Observatory, Charlottesville, Va., U.S.A. The suggestion was first made in 1971 that a symposium on interstellar grains would be timely. The response to the first preliminary announcement, which was sent out on November 29, 1971, was well beyond our expectations. The meeting was locally sponsored by the State University and by Dudley Observatory. The National Aeronautics and Space Administration and the National Science Foundation con tributed along with the JAU. There were 158 participants of whom 49 were from 15 countries outside the United States. A total of 92 papers were presented.

This written account of the Symposium on Planetary Nebulae was prepared from manuscripts submitted by the participants. Nearly every paper that was presented at the meeting is reproduced here, in either complete or abbreviated form. The dis cussions have been somewhat shortened and rearranged, but we have tried to preserve the essential points and the general tenor of the exchanges. Participants who spoke in the discussion were asked immediately for written remarks, which were then edited, reproduced, and circulated at the meeting by the highly effective local Secretariat organized by Dr Perek. In addition, notes of the discussion taken by Mrs Edith F. Swan and by the undersigned were used. We wish to thank all the authors for their unusually good cooperation. We are especially grateful to Dr Minkowski, who kindly provided many excellent repro ductions of Mount Wilson and Palomar photographs, mostly taken by himself, of various planetary nebulae. We are particularly indebted to Mrs Swan, who attended the Symposium, made notes on the papers and discussions as they occurred, and did much of the checking and editing of the manuscripts. In addition, we are very grateful to Mrs Evelyn Seaver, who also did much of the checking, editing, and retyping of manuscripts, and to Dr B.L. Webster, Miss Rebecca Todd, Mr Joseph Tapscott, and Mr Dennis Schatz, who provided excellent assistance in the preparation of this volume.

The First Conference of the International Society for the Study of Time was held at the Mathematisches Forschungsinstitut at Oberwolfach in the Black Forest, Federal Republic of Germany from Sunday, 31 August to Saturday, 6 September, 1969. The origin of this conference and the formation of the Society goes back to a proposal due to J. T. Fraser that was discussed at a conference on "Interdisciplinary Perspectives of Time" held by the New York Academy of Sciences in January, 1966. It was unanimously agreed than that an international society should be formed on an interdisciplinary basis with the object of stimulating interest in all problems concerning 'time and that this object could best be attained by means of conferences held at regular intervals. J. T. Fraser was elected Secretary, S. Watanabe Treasurer, and I was elected President. It was agreed, at my suggestion, that the organization of the first conference of the newly formed Society be left to a committee of these three officers, on the understanding that they would invite authorities on the role of time in the various special sciences and humanities to form an Advisory Board to assist them. One of the main difficulties in seeking support for an interdisciplinary conference is that most foundations confine their interest exclusively either to the sciences or to the humanities.

P. J. MESSAGE University of Liverpool The papers which comprise this volume were presented at Colloquium No. 41 of the International Astronimical Union, which was held in Cambridge, England, from the 17th to the 19th of August, 1976, and had as its subject 'Dynamics of Planets and Satellites and Theories of their Motion'. The Colloquium was held just prior to the XVIth General Assembly of the Union (which was held from 24th August to 2nd September, in Grenoble, France) to provide an opportunity for the presentation of research papers on a number of active and lively branches of Celestial Mechanics to a gathering of experts in the field, and for the stimulus of discussion of research problems of interest to participants. A number of papers testify to the progress being made in General Planetary Theory, the theories of motion of the minor planets, the Moon, and the satellites of Jupiter and Saturn, and to significant advances in both the general and restricted gravitational problems of three bodies. The Organizing Committee of the Colloquium was comprised of J. Chapront, R. L. Duncombe, J. Hadjidemetriou, Y. Kozai, B. Morando, J. Schubart, V. Szebehely, and P. J. Message (Chairman). The local Organizer was D. C. Heggie, to whose tireless efforts the success of the arrangements is due. IX LIST OF PARTICIPANTS N. Abu-el-Ata, Bureau des Longitudes, 77 Avenue Denfert Rochereau, 75014 Paris, France K. Aksnes, Center for Astrophysics, 60 Garden Street, Cambridge, Massachusetts 02138, U. S. A.

Socrates knew all that was known by his contemporaries. But already in the Middle Ages it was becoming difficult for a single man to have a truly encyclopedic view of all human knowledge. It is true that Pico della Mirandola, Pius II, Leonardo da Vinci, and several other great minds were thoroughly in possession of considerable know ledge, and knew all that one could know, except no doubt for some techniques. The encyclopedists of the 18th century had to be content with an admirable survey: they could not go into details, and their work is a collective one, the specialized science of each collaborator compensating for the insufficiencies of the others. We know very well that our science of today is a science of specialists. Not only is it impossible for anyone person to assimilate the totality of human knowledge, it is impossible even to know ones own discipline perfectly thoroughly. Each year the presses of science pro duce a frightening quantity of printed paper. Even in very limited fields, new journals are created every day, devoted to extremely specialized, often very narrowly defined subjects. It is indeed evident that in a field whose scope extends well beyond astronomical or astrophysical research, it is materially impossible to be informed of everything, even with the richest of libraries at hand.

The Symposium on the Crab Nebula was held in the University of Manchester from 5 to 7 August, 1970. The meetings on the first day were held in the Physics Department on the University campus, and on the second and third days at the Nuffield Radio Astronomy Laboratories, Jodrell Bank. The 4th Symposium of the International Astronomical Union, convened in the University and at Jodrell Bank fifteen years earlier (25-27 August, 1955), dealt with the entire subject of radio and radar astronomy. Now the subject matter of this 46th Symposium of the International Astronomical Union was confined to one single object. It is interesting to recall that even at the 1955 symposium the Crab Nebula figured prominently. In particular, J. H. Oort described the new measurements of the polariza tion of the light from the nebula and I. S. Shklovsky explained the light and radio emission in terms of the motion of relativistic electrons in the magnetic field of the nebula. No one could have foreseen the exciting discoveries of a decade later which stimulated the assembly of 172 participants to this 1970 Symposium. In addition to the lectures and discussions the visitors were able to tour the laboratories and telescopes at J odrell Bank to see the various researches in progress. The demonstrations included a real-time display on a cathode ray tube of the pulses from pulsar CP 0328 received in the 250 ft steerable telescope.

Many aspects of symbiotic stars have long puzzled astronomers. For instance while most students of the subject have considered them binary, many have at different times supported single star models. The nature of their outbursts is uncertain, while the dividing line between symbiotic stars and novae is unclear. In any case doubts can even be raised as to whether a class of "Symbiotic Stars" really exists. Much new data has been obtained in recent years, in particular from the study of radiation outside the visual region. Many symbiotic stars have been studied in the UV with IUE since 1978, while X-rays were det ected in a few cases with the Einstein satellite. There have been a num ber of infrared and radio studies, and the number of known symbiotic stars has also considerably increased. Furthermore theoretical ideas have in recent years been considerably enriched by concepts of stellar winds, and accretion phenomena in binaries including accretion disks. It was there fore extremely opportune and timely to hold the first international meet ing exclusively devoted to these stars, so as to consider the new results from such a wide range of observations in different spectral regions, and the conclusions which can be drawn for possible models as well as theories of the nature and structure of symbiotic stars. After a session devoted to new observations in different spectral regions, a session was spent considering some individual stars."

The subjects of resonance and stability are closely related to the problem of evolution of the solar system. It is a physically involving problem and the methods available to mathematics today seem unsatisfactory to produce pure non linear ways of attack. The linearization process in both subjects is clearly of doubtful significance, so that, even if very restrictive, numerical solutions are still the best and more valuable sources of informations. It is quite possible that we know now very little more of the entire problem that was known to Poincare, with the advantage that we can now compute much faster and with much more precision. We feel that the papers collected in this Symposium have contributed a step forward to the comprehension of Resonance, Periodic Orbits and Stability. In a field like this, it would be a surprise if one had gone a long way toward that comprehension, during the short time of two weeks. But we are sure that the joint efforts of all the scientists involved has produced and will produce a measurable acceleration in the process. If this is true it will be a great satisfaction to us that this has happened in Brasil. The Southern Hemisphere in America has now begun to participate actively in the Astro nomical Society and for this, we are grateful to everyone who has helped."

ix List of Speakers and Participants xi Group Photograph xviii Greetings by B. Garfinkel, A. E. Roy and P. J. Message xix Introduction xxiii PART I: FUNDAMENTAL CONSIDERATIONS OF STABILITY R. BROUCKE/Simple Non-Integrable Systems with Two Degrees of Freedom 3 G. CONTOPOULOS/lnstabilities in Systems of Three Degrees of Freedom 25 R. W. EASTON/Perturbed Twist Maps, Homoclinic Points and Ergodic Zones 41 O. GUREL/Bifurcation Theory and its Applications V. SZEBEHELY/General Considerations of Stability in 49 61 Celestial Mechanics PART II: ASPECTS OF NUMERICAL ANALYSIS AND STATISTICAL MECHANICS S. J. AARSETH/An N-Body Integration Method in Co-Moving Coordinates 69 J. BAUMGARTE/The General Theory of Conservative Stabilization of the Keplerian Problem 81 C. DEWITT-MORETTE /Celestial Mechanics, Quantum Mechanics, and Path Integration 95 G. C. STEY/Statistical Viewpoint in Classical Mechanics 103 PART III: STABILITY OF PLANETARY SYSTEMS ~ C. FROESCHLE and H. SCHOLL/Evolution of Orbits in the Outer Part of the Asteroidal Belt and in the Kirkwood Gaps as Influenced by the Mass Effects of Saturn and Jupiter 115 v TABLE OF CONTENTS vi B. GARFINKEL/On the Stability of Resonant Motion in 121 the Light of the Regularizing Function 129 P. GOLDREICH/The Rings of Saturn and Uranus J. D. HADJIDEMETRIOU/Instabilities in Periodic 135 Planetary-Type Orbits P. J. MESSAGE/Bounds on Secular Terms in Celestial 165 Mechanics A. E. ROY/Empirical Stability Criteria in the 177 Many-Body Problem R. O. VICENTE/Instabilities in Planetary Systems 211 PART IV: THE PROBLEM OF THREE BODIES H.

The idea of the organization of a Symposium on Spiral Structure came at a special meeting of Commission 33 on Spiral Structure during the 12th General Assembly of the IAU in Prague, 1967. So much interest was shown during this meeting that one of us proposed a special Symposium on the 'Spiral Structure of Our Galaxy' for 1969. The response was immediate and it was finally agreed upon holding the Symposium in Basel, a center of galactic research in the center of Europe. During the next months a special 'List of Problems', related to this Symposium, was sent to many prospective participants by the president of Commission 33. This stimulated an increase of interest in problems of galactic spiral structure and a con centrated effort on some problems. The organizing Committee of the Symposium was composed of Drs. L. Woltjer (president), W. Becker, A. Blaauw, B. J. Bok, G. Contopoulos, F. J. Kerr, C. C. Lin, S. W. McCuskey and S. B. Pikel'ner. Most of the work for the organization of the Symposium was carried by Dr. L. W oltjer. The Local Committee, composed of Drs. W. Becker, U. W. Steinlin, R. P. Fenkart, and G. A. Tammann, made every effort to secure the success of the Symposium. Most of the credit goes to Dr. Steinlin. The Symposium was supported financially by the IAU and by the Swiss National Science Foundation. The meetings took place at the University of Basel, which provided also secretarial help and many other facilities."

This volume contains all but one of the lectures and seminars presented at the NATO Advanced Study Institute on HOI Thin Plasmas in Astrophysics held in Cargese, Corsica, from September 8 to 18, 1987. The meeting was planned in collaboration with the members of the Scientific Organizing Committee, 10 whom I am grateful for suggesting a comprehensive and well balanced program. The SOC was comprised of Prof. J. Bleeker (Space Research Institute. Utrecht, The Netherlands), Dr. C. Cesarsky (CEN Saclay, France), Dr. R. Mushotzky (GSFC, USA), Prof. K. Pounds (University of Leicester, UK), Prof. H. Schnopper (Danish Space Research Laboratory, Denmark), Dr. H. Tananbaum (Center for Astrophysics, USA), Dr. G. Trinchieri (Arcetri Observatory, Italy), and Prof. 1. Truemper (MPE, Garching, Germany). The ASI, fully supported by the NATO Scientific Affairs Division, was organized with the intent of providing a critical and up-to-date overview of our present kowledge and understanding of the properties of hot thin plasmas in astrophysics as they are revealed by X-ray observations from space. The X-ray and UV emission from optically thin thermal plasmas is a common feature of many astrophysical systems. This type of emission occurs in the solar corona and in the coronae of other stars, in supernova remnants and in the hot interstellar medium, in normal galaxies and galactic halos, and in the intergalactic gas in clusters.

The principal purpose of IAU Colloquium No. 35 was to discuss those aspects of the techniques of the compilation, evaluation, and distribution of data that are common to astrometry, photometry and spectrometry of stars and stellar systems. In the announcement of the Colloquium, it was suggested that there would be special emphasis on the techniques of quality control, and on the standards for the presentation of numerical data in both printed and com puter-readable form. As the meeting progressed it became clear that the lack of a standard, unambiguous system for the identifi cation of stellar objects was a source of much confusion and inefficiency in the use of existing data files. This and other such matters were the subject of further discussions by Commission 5 at the General Assembly of the International Astronomical Union (IAU), which was held at Grenoble during the following fortnight, 24 August - 2 September 1976. The proposal for the Colloquium was prepared by J. Jung, who was then Director of the Centre des Donnees Stellaires at Stras bourg, and G. A. Wilkins, Chairman of the IAU Working Group on Numerical Data, and was accepted by the IAU Executive Committee on the recommendation of the President of Commission 5, with the support of Commissions 25, 29 and 45. The Scientific Organising Committee consisted of W. Fricke, B. Hauck, C. Jaschek, J. Jung, B. Kukarkin, P. Lacroute, A. Underhill and G. A. Wilkins (Chair man). The Local Organising Committee consisted of A."

After the same pattern as the XIII th General Assembly of the International Astronom ical Union the present Volume of the Highlights in Astronomy contains the texts of the invited discourses given at the XIVth General Assembly held in Brighton, England, August 1970. It contains further the papers and discussion remarks presented at the six joint discussions, as well as the invited papers given at the special session on the Moon. In addition this Volume contains the papers given at the joint meeting of Commissions 24, 27, 30, 33 and 37 on RR Lyrae Stars. It goes without saying that the nearly hundred papers printed in this Volume represent only a minor part of all matter dealt with at the XIVth General Assembly of the Union; the many important discussions that took place in a few hundred commission meetings are not included. For short abstracts and reviews of these the reader is referred to Transactions of the International Astronomical Union XIVB. I wish to thank those who contributed to this Volume for the speed in submitting the manuscripts of their papers. This, together with the efficiency of the Publishers allowed for a rapid publication.

The publication in English of this monograph seems to me to indicate the ever increasing interest of astrophysicists in the physical and dynamical problems of planetary nebulae-one of the most interesting and fruitful branches of theoretical astrophysics. Their interest in part arises from the fact that the methods of identify ing the physical processes occurring in planetary nebulae, as well as the many theo retical results, are now acquiring a degree of uni versality as their sphere of application increases. Finally, the special cosmic significance of planetary nebulae is becoming apparent. The English edition of Planetary Nebulae differs considerably from the Russian version published in 1962, primarily because of the new results included in it, but also because of numerous editorial revisions. The problems of magnetic fields and hydrodynamics in planetary nebulae are beginning to occupy an important place in the study of the dynamics of these objects. Recent studies by D. H. Menzel confirm the idea advanced in the present mono graph as to the existence of magnetic fields in planetary nebulae. New light is being cast on the dynamics of planetary nebulae by the hydrodynamic investigations of F. D. Kahn, W. G. Mathews and others. Unfortunately I was not able to include these and other interesting results in the present edition."

to Mission Design for Geostationary Satellites by J.J. Pocha British Aerospace, Space and Communications Division, Steven age, u.K. D. Reidel Publishing Company A MEMBER OF THE KLUWER ACADEMIC PUBLISHERS GROUP Dordrecht / Boston / Lancaster / Tokyo Library of Congress Cataloging in Publication Data Pocha, J. J. (Jehangir. J.), 1945- An introduction to mission design for geostationary satellites. (Space technology library) Includes bibliographies and index. 1. Geostationary satellites. 2. Artificial satellites in telecommunica tion. I. Title II. Series. TK5104.P63 1987 621.38'0423 87-4909 ISBN-13: 978-94-010-8215-0 e-ISBN-13: 978-94-009-3857-1 DOl: 10.1007/978-94-009-3857-1 Published by D. Reidel Publishing Company, P.O. Box 17, 3300 AA Dordrecht, Holland. Sold and distributed in the U.S.A. and Canada by Kluwer Academic Publishers, 101 Philip Drive, Assinippi Park, Norwell, MA 02061, U.S.A. In all other countries, sold and distributed by Kluwer Academic Publishers Group, P.O. Box 322, 3300 AH Dordrecht, Holland."

The idea of holding a colloquium on Schmidt telescopes (techniques and science) originated from the observation that, in the last ten years and in spite of the remarkable developments and achievements in this field of astronomical research, there had been no specific opportunity for the experts to meet together, make the point on the state of the art, discuss and coordinate future plans. Therefore, Prof. L. Rosino, one of the pioneers in the use of wide-field telescopes, driven also by the wish of honouring the over four decades of activity of the Asiago Observatory, proposed to the Executive Committee of the International Astronomical Union to sponsor a colloquium on 'Astronomy with Schmidt type telescopes I to be held at Asiago at the end of the summer of 1983. Details about the composition of the Scientific Organizing Committee and the sponsoring organizations are given in Prof. Rosino's 'Welcome to the Participants * The granting of this proposal was the beginning of a ' number of headaches tor the members of the Local Organizing Committee, R. Barbon, F. Ciatti, P. Rafanelli and myself. If, organlzationwise, the colloquium was successful, this is truly due to the generous efforts of my colleagues of the SOC and to the efficient organization of the Linta Park, the hotel hosting the meeting.

As it was said by one of the participants to this workshop" In our attempts to understand the spectral evolution of galaxies, we are fortunate indeed to have the ability to look back in time and observe galaxies as they were billions of years ago. Perhaos in no other discipline is it possible to gain such a direct view to hJstory. The galaxies we seek to study are remote, their light faint, and thus only recently has it become technicaJlv feasible to sample the spectra of normal luminosity galaxies at lookback times of five billion years or more" .... or, perhaps. even to see galaxies in the process of their formation. or shortly afterwards. This fourth workshop organized by the "Advanced School ot Astronomy was indeed centered on the "Spectral Evolution of Galaxies." on reviewing and discussing the relevant astrophysical processes and on assessing our current ability to model and understand the evolution of stellar populations. Following an opening session dealing with some outstanding questions of galaxy evolution. Session I addressed the specific problems of galaxy and star formation processes. topics of uncertainty and controversy to which IRAS observations may give novel perspectives. The properties of stellar populations in the local group of galaxies formed the basis of Session II. Session III dealt with the fundaments of the theory of spectral and photometrical evolution of stellar populations. and with recent developments in the theory of stellar structure. a necessary step to model and understand galactic evolution.

The lAU Colloquium No. 56, the Second lAU Colloquium, "On Reference Coordinate Systems for Earth Dynamics," co-sponsored by the COSPAR and the International Association of Geodesy of IUGG was held in Warsaw, Po1and, on September 8-12, 1980. The Co11oquium was organized by the Space Research Centre of the Po1ish Academy of Sciences and the Smithsonian Institution Astrophysica1 Observatory. It was sponsored by the Committee of Astronomy, the Committee of Geodesy, and the Committee of Space Research of the Po1ish Academy of Sciences. The first Co11oquium devoted to this subject was held in Torun, Po1and, in 1974. The Scientific Organizing Committee consisted of: Cochairmen Dr. E. M. Gaposchkin USA Dr. B. Ko~aczek Po1and Members of the Program Committee Prof. J. Kova1evsky France Prof. I. I. Mueller USA Prof. M. Rochester Canada Members Dr. M. Bursa Czechos1ovakia Dr. H. K. Eichhorn USA Prof. W. Fri cke FRG Dr. E. Hog Denmark Dr. Y. Kozai Japan Dr. Y. S. Yatskiv USSR The Loca1 Organizing Committee consisted of: Dr. B. Ko~aczek, Chairman Dr. W. Pache1ski, Secretary Dr. W. Dobaczewska Dr. J. Krynski Dr. G. Sitarski Prof. J. Smak Dr. J. B. Zielinski Mr. W. Zarnowiecki ix E. M. Gaposchkin and B. Kotaczek (eds. ), Reference Coordinate Systems for Earth Dynamies, ix-x. Copyright (c) 1981 by D. Reidel Publishing Company. x PREFACE The duties of chairmen of the sessions were performed by Dr. J. Zielinski, Dr. P. Bender, Prof. W. Fricke, Dr. B.

The three years since the Brighton General Assembly have been the most active period in the history of the Union. 33 IAU Symposia and Colloquia, the first Regional Meeting under the Auspices of the IAU, several co-sponsored Meetings and many other special projects. All this culminating with two General Assemblies in two opposite parts of the Earth, Australia and Poland. At the same time the membership of the Union rose to 3200, the number of Commissions to 40, the number of adhering countries to 47. The present Volume gives a general picture of the Union's recent activity. It contains the report of the Executive Committee, the report of the General Assembly, including the Commissions, Meetings, a short report on the Extraordinary General Assembly and an Appendix with the Members and Commissions of the IAU and the approved names of Lunar and Martian features. I take this opportunity to thank all our collaborators, members of the Executive Committee, Presidents of Commissions, Chairmen of Specific Projects, IAU Secrt;taries and all the Members of the IA U for their contribution to keep our Union a living body of active scientists and a big inter national family. G. CoNTOPOULOS General Secretary CONTENTS Page No."

This book is an outgrowth of the notes made for the semester lectures on 'Problems of Extragalactic Astronomy' given almost annually during two decades at the Ob- servatorio Astronomico of the Universidad de Cordoba. Shorter versions were also given at La Plata, Santiago de Chile, Sao Paulo, Rio de Janeiro and Paraiba. E. Scalise made a Portuguese language version of the notes and encouraged me to publish them; although my friend J. Kleczek is to be blamed for the idea of this book. Not every subject on Extragalactic Astronomy has been touched in this book: instead I have followed those which interested me during 25 years of professional practice in this part of the world. I acknowledge helpful suggestions from M. Pastoriza and G. Carranza, the com- prehension of Director L. Milone, and the collaboration of the staff of the Observa- tory in Cordoba. R. Tschamler's humor and wit made light the task of producing the English version and M. Pizarro's devotedness produced the edited MS. To both of them I am in deep gratitude. "A book is published out of necessity, otherwise the author would spend his entire life polishing the originals" was the answer given by J. L. Borges to an inquisi- tive journalist. These words explain why this book is so different from the lecture notes, and also from the book I was hoping for. I thank B. McCormac and the D. Reidel Publ. Co. for my salvation from Borges' inferno.