The idea of this Colloquium came during the XVIIth General Assembly of the I. A. U. at Montreal. The meeting was organized under the auspices of I. A. U. Commission 5 (Documentation and Astronomical Data). The Scientific Organizing Committee consisted of C. Jaschek (chairperson), O. Dluzhnevskaya, B. Hauck (vice chairperson), W. Heintz, P. Lantos, Th. Lederle, J. Mead~ G. Ruben, Y. Terashita, G. Wilkins. The members of this Committee are to be thanked for their devotion to the organization of what turned out to be a very successful meeting. The program was organized so as to cover most of the aspects concerning work with machine readable data. In a certain sense it is the develop ment of the subjects of I. A. U. Colloquium 35 "Compilation, critical evaluation and distribution of stellar data" held at Strasbourg in 1976. The meeting was opened by welcoming addresses delivered by Dr A. Florsch, Director of the Strasbourg Observatory, Prof. H. Curien, President of the European Science Foundation and Prof. W. Heintz, President of I. A. U. Commission 5. The sessions were devoted to the fol lowing subjects : Existing data centers, Data networks, New hardware, Recent software developments, Bibliographical services, Copyright, Editorial policies and nomenclature, Data in astronomy and Data in space astronomy. The different sessions were chaired by G. A. Pilkins, J. Mead, S. Lavrov, W. Heintz, P. Lantos, M. McCarthy, J. Delhaye and G. Westerhout. On July 9. Dr A.

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.

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.

The yearbook series Reviews in Modern Astronomy of the Astronomische Gesell three years ago in order to bring the scientific events schaft (AG) was established of the meetings of the society to the attention of the worldwide astronomical community. Reviews in Modern Astronomy is devoted exclusively to the invited reviews, the Karl Schwarzschild lectures, and the highlight contributions from leading scientists reporting on recent progress and scientific achievements at their research institutes. Volume 4 comprises all, eighteen contributions which were presented during the fall meeting of the AG at Preiburg/Breisgau in September 1990. They cover problems in solar research and the solar system as well as the first results of the ROSAT and Hipparcos space missions, stellar and extragalactic studies, and Supernova 1987A in the Large Magellanic Cloud. The Karl Schwarzschild Medal was awarded to Professor Eugene Parker1. His lecture entitled "Convection, Spontaneous Discontinuities, and Stellar Winds and X-Ray Emis*sion" begins this volume.

The Little Book of Stars answers, in the clearest language, the questions anyone might have about our heavenly canopy. How are stars born? How do they die? Why do they shine? How long do they shine? Is our star, the Sun, dying? How can you tell time from the stars? Or navigate? What are the measures of stars? Can we ever travel to other stars? In this engagingly written and concise book, the second in the Little Book series, noted astronomer James B. Kaler shows us "the significance that the stars have had in human life, how we have used them to tell our stories, and how we use them to find who and where we are."

This book, in three parts, describes three phases in the development of the modern theory and calculation of the Moon's motion. Part I explains the crisis in lunar theory in the 1870s that led G.W. Hill to lay a new foundation for an analytic solution, a preliminary orbit he called the "variational curve." Part II is devoted to E.W. Brown's completion of the new theory as a series of successive perturbations of Hill's variational curve. Part III describes the revolutionary developments in time-measurement and the determination of Earth-Moon and Earth-planet distances that led to the replacement of the Hill-Brown theory in 1984.

This volume contains the detailed text of the major lectures and the abstracts of the lectures delivered during the seminar sessions. The subject of our NATO Advanced Study Institute in 1981 was the Application of Modern Dynamics to Celestial Mechanics and Astrodynamics. This Preface will first explain the terminology, then it will review shortly the content of the lectures and will outline how all this was made possible and, finally, it will disclose our future aspirations. Periodicity is an extremely important concept in our field, therefore, it should not be unexpected that our NATO Advanced Study Institute is enjoying a period of three years. Since 1972 we conducted four Institutes with increasing interest and en thusiasm displayed by the participants, lecturers and by this Director. Celestial Mechanics or Dynamical Astronomy is part of Astronomy dealing mostly with the motion of natural celestial bodies. Astrodynamics or Orbital Mechanics is the application of dynamics to problems of Space Engineering and it treats mostly the dynamical behavior of artificial satellites and space probes. The underlying mathematical and dynamical principles are, of course, the same for Celestial Mechanics and for Astrodynamics. This Director of the Institute and Editor of the Proceedings was extremely fortunate to have obtained the cooperation of out standing lecturers who were clear, thorough, understandable, patient to answer questions, but above all, had knowledge of the ix V. Szebehely (ed.). Applications of Modern Dynamics to Celestial Mechanics and Astrodynamics. ix-x."

In the twenties the new atomic physics opened the way toward a quantitative interpretation of stellar spectra. It was one of the aims in this new branch of astrophysics to determine in a quantitative way the chemical composition of stellar atmospheres, i. e. of those parts of the stars which are accessible to spectro scopic observation. It was only in the forties that the first reasonably accurate and complete analyses became available. In the meantime nuclear physics and the theory of the internal constitution of the stars had reached the important conclusion that the main sequence of the Hertzsprung-Russell-diagram is taken up by stars which in their central parts produce energy by the conversion of hydrogen into helium. It was BAADE who in the early fifties stimulated observational and theoretical work concerning the colour-magnitude-diagrams of star clusters and their connection with the nuclear evolution of stars. Obviously, this type of research opened also the way towards much more difficult and far reaching fields of research: the formation of galaxies and the origin of the chemical elements and their abundance distributions."

Interstellar matter is one of the most active fields of research in present-day astronomy. Observational information spans the full electromagnetic spectrum from gamma rays through rocket-ultraviolet, optical, infrared and millimeter to long radio waves. Results of research in physical chemistry find as much application as mathematical methods. Interstellar matter plays a leading role in studies of our Galaxy and of external galaxies, and contributes increasingly to stellar astronomy. At the 16th General Assembly of the International Astronomical Union, held in August 1976 in Grenoble, France, the many new developments in this vast field were surveyed in a number of sessions of Commission 34 (Interstellar Matter), mostly jointly with other Commissions of the Union. Separate sessions were devoted to: The hot interstellar gas phase, Interaction of stars and interstellar medium, Interstellar molecules and dust, The large-scale distribution of interstellar matter in the Galaxy, and Interstellar matter in external galaxies. Twenty-four invited review papers were presented and discussed in these sessions. The quality and success of these topical reviews made it seem desirable to make them available to a wider audience. Professor Edith Muller, the new General Secretary of the IAU, enthusiastically supported the idea. Most importantly, the reviewers - who had originally been pro mised that an oral paper was the only requirement - agreed to prepare written versions. I am grateful to Mrs. Muller, to the authors, and to Reidel Publishing for their collaboration in the preparation of this book."

Little more than ten years have passed since spaceprobe-borne instruments con clusively demonstrated the existence of the solar wind. These observations con firmed the basic validity of a theoretical model, first proposed by E. N. Parker, predicting a continuous, rapid expansion of the solar corona. The subsequent decade has seen a tremendous growth in both the breadth and sophistication of solar wind observations; the properties of the interplanetary plasma near the orbit of the earth are now known in great detail. The theory of the coronal ex pansion has also been highly refilled both in the sense of including additional physical processes, and of treating more realistic (time-dependent and non spheri cally-symmetric) coronal boundary conditions. The present volume is an attempt to synthesize the solar wind observations and coronal expansion models from this decade of rapid development. The ultimate goal is, of course, the interpretation of observed solar wind phenomena as the effects of basic physical processes occurring in the coronal and interplanetary plasma and as the natural manifestations of solar properties and structures. This approach implies an emphasis upon the "large-scale" features revealed by the observations. It requires extensive use of the concepts and methods of fluid mechanics."

For the last few years astrophysicists and elementary particle physicists have been working jointly on the following fascinating phenomena: 1. The solar neutrino puzzle and the question: What happens to the neutrinos on their way from the sun to the earth? 2. The growing evidence that our universe is filled with about 10 times more matter than is visible and the question: What is dark matter made of? 3. The supernovae explosions and the question: What do neutrinos tell us about such explosions and vice versa? The experimental investigation of these phenomena is difficult and involves unconventional techniques. These are presently under development, and bring together such seemingly disparate disciplines as astrophysics and elementary particle physics on the one hand and superconductivity and solid-state physics on the other. This book contains the proceedings of a workshop held in March 1987 at which the above subjects and their experimental investigation were discussed. The proposed experimental methods are very new. They involve frontier developments in low temperature and solid-state physics. The book should be useful to researchers and students who actively work on these subjects or plan to enter the field. It also offers the non-expert reader with some physics background a good survey of the activities in this field.

This book is the fifth volume under the title Organizations and Strategies in Astronomy (OSA). These OSA Books are intended to cover a large range of fields and themes. In practice, one could say that all aspects of astronomy-related life and environment are considered in the spirit of sharing specific expertise and lessons learned.

This book offers a unique collection of chapters dealing with socio-dynamical aspects of the astronomy (and related space sciences) community: characteristics of organizations, strategies for development, operational techniques, observing practicalities, educational policies, public outreach, publication studies, research communication, evaluation procedures, research indicators, national specificities, contemporary history, and so on.

The experts contributing to this book have done their best to write in a way understandable to readers not necessarily hyperspecialized in astronomy while providing specific detailed information and sometimes enlightening lessons learned sections. The book concludes with an updated bibliography of publications related to socio-astronomy and to the interactions of the astronomy community with the society at large.

This book will be most usefully read by researchers, teachers, editors, publishers, librarians, sociologists of science, research planners and strategists, project managers, public-relations officers, plus those in charge of astronomy-related organizations, as well as by students aiming at a career in astronomy or related space science.

The book includes a CD-ROM containing the visionary and fascinating work of L. Pe ek as a space artist.

"More than anything else, Organizations and Strategies in Astronomy is about change, recording where we've been and how we have evolved, and extrapolating to where we will be in the coming decades." Caty Pilachowski, outgoing President of the AAS"

It is sometimes said that astronomy is the crossroads of physics. In the same spirit, it can forcefully be argued that galaxies are the crossroads of astronomy. Internal pro ces ses within galaxies involve all of the fundamental components of astrophysics: stellar evolution, star formation, low-density astrophysics, dynamics, hydrodynamics, and high-energy astrophysics. Indeed, one can hardly name an observational datum in any wavelength range on any kind of celestial object that does not provide a useful clue to galaxy formation and evolution. Although internal processes in galaxies until recently occupied most of our attention, we now know that it is also vital to relate galaxies to their environment. How galaxies congregate in larger structures and are in turn influenced by them are crucial questions for galactic evolution. On a grander level we have also come to regard galaxies as the basic building blocks of the universe, the basic units whereby the large scale structure of the universe is apprehended and quantified. On a grander level still, we also believe strongly that galaxies are the direct descendents of early density irregularities in the Big Bang. Galaxy properties are now viewed as providing a crucial constraint on the physics of the Big Bang and a vital link between the macroscopic and microscopic structure of the universe."

This work deals with some of the most typical complexes of interstellar matter and is intended to serve both as a reference book for the specialist and as an introduction for the newcomer to the field. It is hoped to meet the first aim by presenting a holistic view of the well studied complexes in Orion, built on information derived from various branches of modern Astrophysics. The wealth of published data is presented in the form of photographs, contour maps, diagrams and numerous heavily annotated tables. The second aim is pursued by providing an outline of the complexes, the physical problems associated with them, the empirical models describing their be haviour and, in addition, by including an extended Appendix section summarizing the numerous methods employed to derive the physical parameters of an H II region and the dust and molecular cloud physically associated with it. The book consists of five chapters and four Appendix sections. Chapter 1, which is concerned with the large scale view of the Orion region, outlines the morphology of the area and examines in particular the nature of Barnard's Loop and the associated filamentary structure in addition to the origin of the I Orion OB association. Chapter 2 focuses on the ionized gas of the Orion H II/molecular complex i. e."

The idea of this colloquium was first put forward by Prof. P. Keenan when he visited the Centre de Donnees Stellaires, in September 1982. Dr. A. Florsch, Director of the Strasbourg Observatory, kindly accepted to field it at Strasbourg. The scientific organization of the colloquium was in charge of a Committee chaired by Prof. P.C. Keenan and composed by M. Feast, A. Florsch, B. Gustafsson, D. Harmer, M. Jaschek (secretary), R. McClure, A. Maeder, W. Straizys and T. Tsuji. The members of the Committee helped to translate the idea into a very successful meeting. It should be added that this colloquium was the first meeting devoted to late-type peculiar stars. The program was organized by sessions devoted to the following topics : taxonomy, photometric properties, distribution and space motions, chemical com- position, model atmosphere, binary systems and evolutionary tracks. Each session started with a review paper, followed by contributed papers presented as posters. The different sessions were chaired by W. Bidelman, R. Cayrel, Ch. Cowley, A. Heck, H.R. Johnson, J.P. Kaufmann and T. Tsuji, who did an excellent job. The President of the "Louis Pasteur University of Strasbourg", Prof. H. Duranton, welcomed the participants to the University where the sessions were held; Dr. A. Florsch welcomed the participation on be.balf of the French astrono- mical community and Prof. P. Keenan spoke on behalf on the Scientific Organizing Committee.

This book contains the lectures presented at the Summer Advanced Study Institute, 'Earth's Particles and Fields' which was held at the University of Sheffield, England, during the period August 13-24, 1973. One hundred thirty nine persons from sixteen different countries attended the Institute. The authors and publisher have made a special effort for rapid publication of an up-to-date status of the particles, fields, and processes in the Earth's magnetosphere, which is an ever changing area. Special thanks are due to the lecturers for their diligent preparation and excellent presentations. The individual lectures and the published papers were deliberately limited; the authors' cooperation in conforming to these specifications is greatly appreciated. The contents of the book are organized by subject area rather than in the order in which papers were presented during the Institute. Many thanks are due to Drs Rolf Bostrom, J. Ronald Burrows, Robert W. Fredricks, Thomas R. Kaiser, Bernt N. Maehlum, Christopher T. Russell, and Martin Walt who served as session chairmen during the Institute and contributed greatly to its success by skillfully directing the discussion period in a stimulating manner after each lecture.

20* * 0 0_ >.1

M. M. Shapiro and J. P. Wefel AN OVERVIEW OF COSMIC RAY RESEARCH: COMPOSITION, ACCELERATION AND PROPAGATION J. P. Wefel PROPAGATION AND TRANSFOR'1ATIONS OF cosme RAYS: 41 FROM SOURCES TO EARTH R. Silberberg, C. H. Tsao, J. R. Letaw and M. M. Shapiro 71 ULTRA HEAVY NUCLEI IN THE COSMIC RADIATION W. R. Binns GALACTIC COSMIC RAY HYDROGEN AND HELIUM 91 J. J. Beatty COSMIC RAYS OF THE HIGHEST ENERGIES 97 J. Szabelski STARS AND COSMIC RAYS 105 I. COOL STARS T. Montmerle STARS AND COSMIC RAYS 131 II. HOT STARS T. Montmerle ON THE POSSIBLE CONTRIBUTION OF WC STARS TO ISOTOPIC 153 ANOMALIES IN COSMIC RAYS AND METEORITES J. B. Blake and D. S. P. Dearborn GAMMA-RAY VIEWS ON THE GALACTIC COSMIC-RAY DISTRIBUTION 163 H. Bloemen VlIl RADIO ASTRONOMY AND COSMIC RAYS 175 K. W. Weiler PARTICLE ACCELERATION IN GALACTIC SUPERNOVA REMNANTS 205 D. A. Green PULSARS AS COSMIC RAY PARTICLE ACCELERATORS -- NEW RESULTS 215 ON THE DYNAMICS OF PROTONS IN VACUUM FIELDS K. o. Thie1heim CONDITIONS FOR ACCELERATION OF SUPER-HIGH ENERGY COSMIC RAYS 227 IN ACTIVE GALACTIC NUCLEI W. H. Sorrell COSMIC RAYS AND A STABLE HYDROSTATIC EQUILIBRIUM OF THE GALAXY 235 H. B10emen VRE AND URE GAMMA P Y OBSERVATIONS BY GROUND BASED 241 DETECTORS W. Stamm 15 HADRON AND MUON COMPONENTS IN PHOTON SHOWERS AT 10 eV 255 Ch. P. Vankov and J. N. Stamenov MONOPOLES, MUONS, NEUTRINOS AND CYGNUS X-3 261 M. L. Cherry, S. Corbato, D. Kieda, K. Lande, and C. K.

With the discovery of pulsars, quasars, and galactic X-ray sources in the late 60's and early 70's, and the coincident expansion in the search for gravitational waves, rela tivistic gravity assumed an important place in the astrophysics of localized objects. Only by pushing Einstein's solar-system-tested general theory of relativity to the study of the extremes of gravitational collapse and its outcomes did it seem that one could explain these frontier astronomical phenomena. This conclusion continues to be true today. Relativistic gravity had always played the central role in cosmology. The discov ery of the cosmic background radiation in 1965, the increasing understanding of matter physics at high energies in the decades following, and the growing wealth of observations on the large scale structure meant that it was possible to make increasingly detailed mod els of the universe, both today and far in the past. This development, not accidentally, was contemporary to that for localized objects described above."

Adriaan Blaauw; Emeritus Professor of Astronomy at the Universities of Groningen and Leiden, former Directo.r of the Kapteyn Laboratory and of the European Southern Observatory, celebrated his 70th anniversary on 12 April 1984. To mark this event, an international Symposium was con- vened on the subject "Birth and Evolution of Massive Stars and Stellar Groups", a subject which has played the leading role in Blaauw's scien- tific research. The present volume contains the Scientific Proceedings of that Symposium. The meeting was organized by a Committee consisting of: W.H.W.M. Boland (Secretary), W.N. Brouw, W.B. Burton, E.P.J. van den Heuvel, H. van der Laan and H. van Woerden (Chairman). Together, these six persons represented the Executive Committees of the Netherlands Foundation for Astronomical Research (ASTRON) and the Netherlands Foundation for Radio Astronomy (RZM), two organizations in which Blaauw has held key offices. The scientific program was planned in full consultation with Adri- aan Blaauw himself. Only section 5, "A profile of Adriaan Blaauw", was kept secret to him. The other four sections: Structure of star-forming regions, Stellar content of young groups, Evolution of massive stars, and Extragalactic perspective on star formation, each represent an im- portant aspect of the overall theme of the Symposium. The program in- cluded 6 major review papers, 18 invited papers, 17 contributed papers, some of which were given as posters, and ample time for discussion.

The papers in this volume were delivered and responded to at the Third Conference of the International Society for the Study of Time. The meeting took place during sunny days, punctuated by an occasional brief storm, in the confer ence facilities of the OEsterreichisches College in Alpbach, Austria, from ]uly 1 to ]uly 10, 1976. In the middle of it came ]uly 4, the 200th anniversary of the Declaration ofindependence, and in honor ofparticipants from the United States there was a special session of papers on the subject of Freedom and Time. [See Fraser, Park in this volume. ] The effect of the papers was kaleidoscopic; reading the table of contents one can surmise the experience of those enthusiasts, and there were several, who heard them all. I think that most people who have been puzzled about time will agree that it is not clear wh at the puzzle is or from what direction the insights will come that will enable us to understand the situation a litde more clearly. As one of the participants wrote afterwards, "After all , we do not know apriori whether there exists areal unity in studies about time, but if one exists it must reveal itself progressively in the course of successive experiences such as these lectures. If it were easy to find, it would have been found already without the Society's help.

The year 1973 marked the highest peak of IAU activity up to now. Besides the Gen eral Assembly in Sydney, and the Extraordinary General Assembly in Poland, there were held eleven IAU Symposia and one Colloquium. Several IAU Publications cover this activity. The Proceedings of the Symposia are published in separate Volumes, while the Transactions of the General Assembly and of the Extraordinary General Assembly contain short reports of the Commission meetings, the administrative sessions, and the opening ceremonies. The present Volume covers some of the scientific Highlights of the General As sembly and of the Extraordinary General Assembly. It contains five Invited Dis courses given in Sydney and Poland, some selected papers, and the Joint Discussions at the General Assembly of Sydney. Of course, there were many more papers of special interest presented in Sydney that could not be included in this Volume. Their titles can be seen in the reports of the various Commissions. It is regrettable that the Invited Discourses of C. H. Townes (Interstellar Molecules) and F. J. Low (Infrared Astronomy) were not submitted for publication. Also only five papers or abstracts of the Joint Discussion on the 'Origins of the Moon and Satellites' have been available. Despite these minor shortcomings, I believe that the present Volume is faithful to its title: it gives a substantial part of the Highlights of Astronomy in 1973.

This volume contains a series of lectures presented at the 4th Course of the International School of Astrophysics, held in Erice (Sicily) from July 9 - July 20, 1977 at the "E. Majorana" Centre for Scientific Culture. The course was fully supported by a grant from the NATO Advanced Study Institute Programme. It was attended by 82 participants from 15 countries. Even though the infrared portion of the electromagnetic spectrum covers an extensive interval from the red region of the optical spectrum (10,000 A) to the microwave radio region (1 mm), its role in astronomy has been minimal until the last two decades. Until very recently, the only objects observed were the sun, the moon and the planets. A primary reason for this late development was the lack of sensitive detectors and the necessary cryogenic technology that must accompany their use. Recent progress in this technology has been paralleled by an ever increasing interest of astronomers in infrared observations, leading to a number of ex tremely important results in different branches of astronomy. This becomes evident when one realizes that in many astrophysical conditions most of the energy is found to be channeled into the infrared portion of the electromagnetic spectrum. Stars were detected that yield most of their radiation in the infrared; these objects present a new view of stellar evolution, both in the birth and death stages."

The publication of this book is extremely timely, for the next major advances in manned space flight after Project Apollo will most likely be made in earth orbital operations. Manned exploration of the moon will certainly continue after the initial landing, but it will be performed essentially with the Saturn V launch vehicles and Apollo spacecraft developed in Apollo, especially in the early phases. Modifications to this basic hardware will increase operating capabilities to permit extensive lunar explo ration during prolonged stay times by the astronauts on the moon's surface. Manned orbital space stations have been studied for years, and NASA is already well along in development of its first attempt to provide more spacious accommo dations for astronaut-scientists in its Saturn Workshop program. While the Workshop is certainly not the ultimate space station of which our technology is capable, it is a workable, poor man's approach to the immediate need for using and expanding our present manned space flight capability without a de trimentalloss of momentum. The approach of converting a Saturn rocket stage into a manned laboratory and observatory in space is an improvisation that matches the use of the jerry-built Jupiter C back in 1958 to launch Explorer I. Let's hope that it can get the job done just as effectively."

The following text forms the proceedings of a conference. It is supposed to contain what was actually reported and discussed, though it does this, one hopes, in a polished and organized way. A sense of actuality, a reporting quality, makes this book different from a collection of review papers as, for example, a book in the series on Stars and Stellar Systems. All Invited Reports have been included as the Reporters wrote them. The Editor's task has been restricted to improving the presentation, a process which in most cases involved only minor revisions. In a few Reports the Editor did some heavy rewriting; in those cases he checked with the Reporters. Obviously a different course had to be taken with respect to the Discussions. They were recorded on tape, transcribed verbatim and then passed back to the discussants. After the discussants returned their versions, the Editor rearranged and condensed the texts and made a considerable effort to provide references. (Unfortunately he was not able to locate all relevant Russian papers from 1968 and 1969. ) The Editor takes the responsibility for mistakes made in this process, which may have produced occasionally his own 'mix-master Universe'. Actually only a few discussion remarks were rejected, more often because of incomprehensibility, rather than because the remark was far from the subject of the Symposium, or was too long, or was too trivial. A few very long remarks have been condensed and put at the end of a Discussion.