One of the most fundamental discoveries of the solar system was the detection of four moons in orbit around Jupiter by Galileo Galilei in 1610. The discovery was significant not only in the context of Jupiter; it gave credence to and was instrumental in firmly establishing the heliocentric system of Nicolaus Copernicus. Almost four centuries after Galileo's discovery, exten sive observations by the two Voyager spacecrafts have once again revolu tionized our thinking about the major planets, their composition, structure, origin, and evolution. This book is an attempt at summarizing our present understanding of the atmospheres and ionospheres in the outer solar system, with particular emphasis on the relevant physics and chemistry. I was motivat ed to prepare this manuscript for the following reasons. First, after under going rapid expansion in the recent past, the subject has finally attained suf ficient maturity to warrant a monograph of its own. Second, I have felt that as a result of recent observations, new and challenging problems have arisen whose resolution requires unconventional analysis and theoretical interpreta tion of existing data, as well as the collection of new kinds of data. I believe the time is ripe to put these issues in the appropriate scientific perspective, with the hope of stimulating novel theoretical, observational, and laboratory studies. I have highlighted the significant scientific problems throughout the book, especially at the end of each chapter.

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.

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.

Planet Earth is part of our Galactic environment, not just the product of it, and it is still today influenced by phenomena related to Galactic forces. Specifically, our planet is affected by its near environment, in particular the small bodies in the Solar System. This book reviews the processes which cause the collisions of these small bodies with the Earth as well as the consequences of such collisions. The various articles take the reader through the Galaxy-Solar System connection to the orbital dynamics of the small bodies and to their number and distribution in near-Earth space. The hazards of the impacts of small bodies on Earth are evaluated, and the geophysical records of such impacts are discussed. The book takes the reader to the forefront of research on both impact cratering and the origin and evolution of small bodies in the Solar System. Thus it brings together two subjects, geophysics and astronomy, which are usually discussed in separate volumes but are closely knit together in this particular area of research.

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."

Infrared Astronomy is a relatively new subject but it has already radically altered our ideas about astronomical sources. Recent progress in this subject is the result of improved detection techniques, particularly the use of detectors at liquid helium temperatures. Unfortunately, the terrestrial atmosphere greatly restricts Infrared astronomers by allowing them to detect radiation only in narrow transmission win dows and by presenting a foreground emission which limits the faintness of observable sources. It is only from aircraft or balloon altitudes that we can begin to observe faint sources over the complete range of wavelengths between the visible and the radio regions. Few such observations have yet been made and none from satellites, although the latter vehicle will offer complete freedom from atmospheric effects. New developments and intermediate steps will be required before the ultimate aim of flying in space can be achieved. It is not surprising therefore that the Fifth Eslab/Esrin Symposium should deal with this problem. This book contains the proceedings of the Symposium and faithfully records all discussions. The Symposium covered the present situation and future perspectives of IR techniques. International leaders in the field reviewed the results to date and the possible developments in telescope systems, detectors, cryogenics, filters, and interferometers. Individual con tributions were made by European and U. S. scientists in each of these fields."

Interest world-wide in the provision of new observational astro nomical facilities in the form of ground-based optical telescopes of large aperture has never been higher than exists at present. The benefits to be gained from increased aperture size, however, are only utilised effectively if efficient instrumentation is also available. There have been significant improvements recently in this area, part icularly in detector technology and data handling as well as in optical design, so that systems which are currently being developed have the capability of being vastly more powerful in terms of the efficient use of photons than those which existed only 5 years ago. The rationale for the decision by Commission 9 of the International Astronomical Union to hold IAU Colloquium 67, therefore, was to obtain reports on these developments with the emphasis placed upon overall efficiency of the complete observational system - from telescope aperture right through to detector output. A fitting venue for the meeting was the site of the 6 metre BTA (Bolshoi Azimuth Telescope) at Zelenchukskaya in the Caucasus mount ains, USSR. The BTA is operated by the Special Astrophysical Observatory located at Nizhnij Arkhyz, a few kilometres from the telescope itself."

This volume contains papers presented at IAU Colloquium No. 90. at the Crimean Astrophysical Observatory in May of 1985. A few additional contributions are included from authors who for various reasons were unable to attend the meeting. Four years have passed since the last major international conference on chemically peculiar stars of the upper main sequence was held in Liege. Belgium in 1981. Previous conferences were held in 1975 (Vienna. Austria) and in 1965 (Greenbelt. Maryland. USA). As the proceedings of this Colloquium show. the recent availability of ultraviolet spectra of large numbers of normal and chemically peculiar A and B stars is having a major impact on the way we study these objects. and has led to many new. exciting and unanticipated results. Simultaneously. the more traditional study of optical spectra has been advanced through the increasing use of very high spectral resolution with high signal-to-noise detectors. The chemically peculiar (CP) stars on the upper main sequence belong in the standard framework within which we understand stellar evolution and the history of matter. Recent work has made it clear that the unusual chemistry and magnetic structure of these objects is of relevance across the broad domain of stellar astronomy. from the upper main sequence to horizontal branch stars and white dwarfs. Metal poor (J>. Boo) as well as metal rich (Ap. Am) stars are an integral part of the picture.

A physicist and an inventor, Jules Janssen (1824-1907) devoted his life to astronomical research. He spent many years traveling around the world to observe total Solar eclipses, demonstrating that a new era of science had just come thanks to the use of both spectroscopy and photography, and persuading the French Government of the necessity of founding a new observatory near Paris. He became its director in 1875. There, at Meudon, he began routine photographic recordings of the Sun surface and had a big refractor and a big reflector built. Meanwhile, he also succeeded in building an Observatory at the summit of Mont-Blanc. The story of this untiring and stubborn globe-trotter is enriched by extracts of the unpublished correspondence with his wife. One can thus understand why Henriette often complained of the solitude in which she was left by her peripatetic husband: "There are men who leave their wives for mistresses; you do it for journeys!" ... Basking in the glow of his success, Janssen was able to undertake the construction of the great astrophysical observatory of which he had dreamed. It was at Meudon that he had it built.

If Zdenek Kopal Department of Astronomy University of Manchester Your Magnificences, my Lord Mayor, ladies and gentlemen! It is a great pleasure for me to respond, on behalf of your foreign guests, to your gracious words of welcome; and to thank you for the wonderful reception which you nave extended to us. The city of Bamberg and its Remeis Sternwarte nas indeed been renowned allover the world for a great many years - as the place where your Observatory's first director, Professor Ernst Hartwig (1851-1923) - in addition to his other titles to fame - collaborated (with Gustav Muller of Potsdam) on the construc- tion of the monumental Geschichte und Literatur des Lirhtwechsels der Veranderlichen Sterne, which since 1918 has (together with its sub- sequent continuation) been a veritable vade-mecum of a1l students of variable stars; where the second director, Professor Ernst Zinner (1886-19]~ prepared his valuable Katalog der Verdachtigen Veranderlichen Sterne (192@ which safeguarded many an astronomer (including the present speaker in the days of his innocence) from premature discovery claims; and whose third director, Professor Wolfgang Strohmeier, initiated in 1959 the tradition of the international colloquia of which ours is the latest successor. It is indeed a great pleasure to welcome Professor Strohmeier - now Emeritus - among us; and to congratulate him on the grace with which he is carrying his years.

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."

Over the last decade many efforts have been made to develop high angular resolution techniques in astrophysics. Combined with imaging facilities, they have rapidly proved their efficiency and have already led to major astrophysical results. During the decade to come, astronomers will be offered new, even more sophisticated high angular resolution tools, especially in the IR and optical domains, coupled with much bigger telescopes, either on the ground or in space. In such a context of rapidly evolving techniques and a growing need for higher angular resolution to test theories or discover new objects, the present book reviews both instrumental and scientific aspects. The main questions addressed are: what kind of science will benefit from high angular resolution techniques? How can they best be used? Audience: The book is accessible to students and research workers in both instrumental and astrophysical aspects.

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Cosmic Update Covers: A novel approach to uncover the dark faces of the Standard Model of cosmology.The possibility that Dark Energy and Dark Matter are manifestations of the inhomogeneous geometry of our Universe.On the history of cosmological model building and the general architecture of cosmological modes.Illustrations on the Large Scale Structure of the Universe.A new perspective on the classical static Einstein Cosmos.Global properties of World Models including their Topology.The Arrow of Time in a Universe with a Positive Cosmological Constant.Exploring the consequences of a fundamental Cosmological Constant for our Universe. Exploring why the current observed acceleration of the Universe may not be its final destiny.Demonstrating that nature forbids the existence of a pure Cosmological Constant.Our current understanding of the long term (in time scales that greatly exceed the current age of the Universe) future of the Universe.The long term fate and eventual destruction of the astrophysical objects that populate the universe --including clusters, galaxies, stars, planets, and black holes.

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Long-term measurements of field strength have been performed over a 160 km path entirely over sea in the Baltic area. For short periods the radio measurements have been combined with meteorolo- gical measurements in order to describe the structure of the re- fractive index field. The heigth of layers was continously deter- mined by remote sensing techniques and their thickness and inten- sity by airborne and balloonborne instruments. From these data, field strengths have been calculated for scatter, reflection and duct propagation. It will be shown that reflection propagation dominates at the low frequency end. Whilst at higher frequencies, very sharp layers are required for reflection propagation. At these frequencies, high signals are generally caused by duct propagation. 1.1 Instruments and plan for the experiments. The radio measurements were performed with the following equipment. 5000 MHz: Transmitted power 500 kW (pulsed). Reflector antennas. Free space field strength over the path + 15 dBm. 460 MHz: Transmitted power 10 W (CW) 8 element Yagi antennas. Free space field strength over the path - 65 dBm. 170 MHz: Transmitted power 10, W(CW). 8 element Yagi antennas. Free space field strength over the path - 60 dBm. The antenna heights for the transmitters and receivers were 100 m above sea level. The field strengths were recorded on ink recorders and simul- taneously sampled, digitized and evaluated on line in a minicom- puter. For the meteorological measurements, the following equipment were used: Airborne microwave refractometer and thermistor, flown up to 2000 m.

by the completion of large aperture synthesis radio telescopes, which have permitted a detailed mapping of radio sources, and by the development of very long base-line interferometry (VLBI), with 4 3 resolutions down to 10- - 10- arc sec, which for the first time has rendered possible radio investigations of the structures of the very compact radio sources found in galactic nuclei and quasars. The observations obtained with this new instrumentation, combined with the work in the optical, infrared and X-ray domain, have made great strides in recent years toward improved testing of radio source models. We feel that the material presented at the Institute represents a rather complete and comprehensive coverage of the present status of studies of non-thermal radio sources, though one is aware of rapid developments in this field of research. The various aspects of this exciting subject were covered in a series of lectures, pre sented in this volume, totaling 44 hours and in 14 topical seminars given by the participants. I wish to express my gratitude to the Scientific Affairs Divi sion of the North Atlantic Treaty Organization for the generous support given to the course. Sincere thanks are also due to Mr. L. Baldeschi for helping with the organization of the meeting and for drawing a number of figures contained in this volume; to Mrs. B. Mandel for the patient typing and help in the editing; and to Mr. R. Primavera for the photographic reproduction of part of the figures."

It is hard to appreciate but nevertheless true that Michael John Seaton, known internationally for the enthusiasm and skill with which he pursues his research in atomic physics and astrophysics, will be sixty years old on the 16th of January 1983. To mark this occasion some of his colleagues and former students have prepared this volume. It contains articles that de scribe some of the topics that have attracted his attention since he first started his research work at University College London so many years ago. Seaton's association with University College London has now stretched over a period of some 37 years, first as an undergraduate student, then as a research student, and then, successively, as Assistant Lecturer, Lecturer, Reader, and Professor. Seaton arrived at University College London in 1946 to become an undergraduate in the Physics Department, having just left the Royal Air Force in which he had served as a navigator in the Pathfinder Force of Bomber Command. There are a number of stories of how his skill with instruments and the precision of his calcula tions, later to be so evident in his research, saved his crew from enemy action, and on one occasion, on a flight through the Alps, from a collision with Mount Blanc that at the time was shrouded in clouds."

Spectral line formation theory is at the heart of astrophysical diagnostic. Our knowledge of abundances, in both stellar and interstellar contexts, comes almost enti rely from line analysis, as does a major fraction of our ability to model stellar atmospheres. As new facets of the universe become observable so the techniques of high reso lution spectroscopy are brought to bear, with great reward. Improved instruments, such as echelle spectrographs, employ ing detectors of high quantum efficiency, have revolutioned our ability to observe high quality line profiles, although until now this ability has been confined to the brightest stars. Fabry-Perot interferometers and their modern deriva tives are bringing new ranges of resolving power to studies of atomic and ionic interstellar lines, and of course radio techniques imply exceedingly high resolution for the cool interstellar medium of molecules and radicals. Telescopes in space are extending the spectral range of these types of observations. Already the Copernicus and IUE high resolution spectrographs have given us a tantalizing glimmer of what it will be like to obtain ultraviolet spectra with resolution and signal to noise ratio approaching those obtainable on the ground. Fairly soon Space Telescope will be producing high resolution spectroscopic data of unparal leled quali ty and distance range. As often happens in astro physics the challenge is now coming from the observers to the theorists to provide interpretational tools which are adequate to the state of the data."

Although there are, in addition to the classic but somewhat dated books'l-, some excellent recent books on ionospheric physics and aeronomy'l-..., their scope is quite different from that of the present monograph. This monograph concentrates on the fundamental physical and chemical processes in an idealized planetary ionosphere as a general abstraction, with actual planetary ionospheres representing special cases. Such an approach appears most appropriate for a concise in troduction to the field, at a time when increasing experimental in formation on the ionospheres of other planets can be anticipated. The main purpose of this monograph, in line with that of the whole series, is to appraise where we stand, what we know and what we still need to know. It is mainly addressed to graduate students and researchers who are in the process of getting acquainted with the field. Within the scope of this monograph it would be impossible to do justice to all relevant publications. Hence, references are somewhat selective and largely limited to the more recent original papers and to authoritative reviews, the latter generally providing also detailed references regarding the historical development of the particular topic. Cgs (gaussian) units are generally used in this book, except where practical units are more appropriate. This book has evolved from a graduate course of the same title which I gave at the Catholic University of America, Washington, D. C."

The material given in this 'Introduction to astronomical photometry' is the subject matter of a lecture at the University of Geneva. It is, therefore, intended for those students, physicists or mathematicians, who have completed their bachelor's degree or diploma, and are intending to work for their Ph.D. in astronomy. We assume then the elementary ideas of astrophysics, magnitude, colour index, spectral classes, luminosity classes, gradient, atmospheric extinction are already known. The student may find it useful to re-read the work of Schatzman [1], Dufay [2] and Aller [254] before embarking upon the study of this 'Introduction to astronomical photometry'. It is not our aim in this book to deal with every aspect of stellar photometry. On the contrary, we shall restriet ourselves to looking at subjects ofwhich knowledge seems to us essential for someone who has to use photometrie quantities in his astronomical research. We are, therefore, keeping the interests of the photometrie measurements user partieularly in mind. We shall only discuss very superficially the technical prob lems and reduction methods for atmospheric extinction. These problems are dealt with very clearly in Astronomical Techniques [3]; the first by A. Lallemand, H. L.

This volume contains the fifteenth tri-annual reports of the Presidents of the forty Commissions of the International Astronomical Union; it refers to the progress in our discipline during the three years 1970, 1971 and 1972. As compared to earlier volumes a gradual change in character is unmistakable. The ever increasing flow of publications, combined with the obvious necessity to keep the Reports at a reasonable size and price level has gradually forced the Commission Presidents to be more selective than before in drafting their Reports. I have certainly stimulated them into that direction - in order that Reports like these be valuable and lasting, it seems imperative that the individual contributions have the character of a critical overall review, where a fairly complete summary is given of the major develop ments and discoveries of the past three years, and in which the broad developments and new trends be clearly outlined, while at the same time essential problems for future research are identified. With respect to the latter item I have suggested the Commission Presidents to add to their reports a brief section on scientific priorities for future research in the field of their Commissions. In order to save space I have suggested to Commission Presidents that references to published papers are given on the basis of their number in the published issues of Astronomy and Astrophysics Abstracts. For instance, the indication (06. 078. 019) or (AAA 06. 078."

The I. A. U. Colloquium No. 29 was held in Budapest, September 1-5, 1975. The subject of the colloquium was: "Multiple Periodic Variable Stars". The colloquium was organized by the Scientific Organizing Committee consisting of W. S. Fitch (Chairman), M. W. Feast, B. V. Kukarkin, P. Ledoux, J. Smak, R. S. Stobie, B. Szeidl, B. Warner and S. C. Wolff. The local organization was placed in the hands of a Committee consisting of the staff of the Konkoly Observatory: B. Szeidl (Chairman), K. Barlai, M. Ill, S. Kany6 and L. Szabados. The colloquium was attended by about 90 scientists representing Australia, Austria, Belgium, Bulgaria, Canada, Czechoslovakia, Denmark, France, F. R. G. , G. D. R. , Greece, Hungary, India, Ireland, Italy, Japan, The Netherlands, New Zealand, Poland, Roumania, South Africa, United Kingdom, U. S. A. and U. S. S. R. Eight sessions were held, viz. 1. . p Canis Majoris Stars. Chairman: W. Wenzel 2. Magnetic and Ap Variables. Chairman: S. C. Wolff 3. Miras and Red Variables. Chairman: P. R. Wood 4. Cepheids. Chairman: R. S. Stobie 5. RR Lyrae Stars. Chairman: B. Szeidl 6. RRs and {) Scuti Stars. Chairman: W. S. Fitch 7. White Dwarfs and Novae. Chairman: B. Warner 8. Close Binaries and X-Ray Sources. Chairman: E. H. Geyer At the beginning of the first session a welcome was presented by Professor G.

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