nd The 2 SORO Workshop on "Mass Supply and Flows in the Solar Corona" was held in Marciana Mariana on the island of Elba, Italy, in the week September 27 to October 1, 1993, as part of a series of workshops planned by the Solar Corona and Particles Working Group of the SOHO Science Working Team (SWT). The purpose of this workshop series is to acquaint the solar community with the capabilities of SORO, and prepare scientific projects and observing plans for the mission. This Workshop, which was at tended by more than one hundred scientists from different countries, focused on the following topics: 1) Fine Scale Structures 2) Loops and Prominences 3) Coronal Streamers 4) Coronal Roles and Solar Wind Each of these four topics was introduced by an observational and a theo retical overview highlighting the most recent advances in their area. A third review illustrated how SORO might help in solving open problems. Oral pa pers and poster presentations were followed by Working Group sessions. On the last day of the Workshop the Group Leaders reported on the activities of their Working Group. These proceedings include most of the papers presented at the Work shop, including the poster papers and Working Group reports by the Group Leaders as well as two overview papers of the SORO mission. All papers have been refereed.

Leading researchers in the area of the origin, evolution and distribution of life in the universe contributed to Exobiology: Matter, Energy, and Information in the Origin and Evolution of Life in the Universe. This volume provides a review of this interdisciplinary field. In 50 chapters many aspects that contribute to exobiology are reviewed by 90 authors. These include: historical perspective of biological evolution; cultural aspects of exobiology, cosmic, chemical and biological evolution, molecular biology, geochronology, biogeochemistry, biogeology, and planetology. Some of the current missions are discussed. Other subjects in the frontier of exobiology are reviewed, such as the search for planets outside the solar system, and the possible manifestation of intelligence in those new potential environments. The SETI research effort is well represented in this general overview of exobiology. This book is the proceedings of the Fifth Trieste Conference on Chemical Evolution that took place in September 1997. The volume is dedicated to the memory of Nobel Laureate Abdus Salam who suggested the initiation of the Trieste conferences on chemical evolution and the origin of life. Audience: Graduate students and researchers in the many areas of basic, earth, and life sciences that contribute to the study of chemical evolution and the origin, evolution and distribution of life in the universe.

Since Luna and Lunar Orbiter photographed the far side of the Moon, the mysterious dichotomy between the face of the Moon as we see it from Earth and the side of the Moon that is hidden has puzzled lunar scientists. As we learned more from the Apollo sample return missions and later robotic satellites, the puzzle literally deepened, showing asymmetry of the crust and mantle, all the way to the core of the Moon. This book summarizes the author's successful search for an ancient impact feature, the Near Side Megabasin of the Moon and the extensions to impact theory needed to find it. The implications of this ancient event are developed to answer many of the questions about the history of the Moon.

K. O. KIEPENHEUER ( Fraunhofer Institut, Freiburg i. Br., Germany) The present symposium, to my knowledge the largest ever held in the field of solar research (170 astronomers from 21 countries) was held in the building of the Hun garian Academy of Sciences in Budapest from September 4 to 8, 1967. It was the 35th symposium organized and sponsored by the International Astronomical Union. The majority of participants were financedfrom national sources. The Organizing Commit tee consisted of K. O. Kiepenheuer (Chairman), L. Davis, L. Dezso (Local Organizer), A.D. Fokker, R. Michard, A.B. Severny, H.J. Smith, Z. Svestka, and H. Tanaka. In order to ensure prompt publication, the manuscripts had to be supplied by the authors 1 month after the meeting. The discussions have been recorded on tape. Their reproduction in this book, however, is based almost completely on the contributors' writing down their comments and questions on the spot. Two special projects have been reported and discussed shortly during the sym posium: The world wide project 'Cooperative Study of Solar Active Regions' (CSSAR) organized by Dr. R. Michard, under the auspices of the IAU, which has put at the disposal of our solar community a precious observing material on Active Regions over a period of 6 months."

Every year Earth is bombarded with about 40,000 tons of extraterrestrial material. This includes microscopic cosmic dust particles shed by comets and asteroids in outer space, meteorites, as well as large comets and asteroids that have led to catastrophic events in the geologic past. Originally considered only a curiosity, extraterrestrial matter found on Earth provides the only samples we have from comets, asteroids and other planets. Only recently mankind has started to actively collect extraterrestrial matter in space (Apollo program, Stardust mission) rather than to wait for its delivery to Earth. Still, most of our knowledge of the origin and evolution of our solar system is based on careful studies of meteorites, cosmic dust, and traces of large impact events in the geologic record such as the mass extinction that terminated the Cretaceous Period and led to the extinction of the dinosaurs. This book summarizes our current knowledge of the properties, origin, orbital evolution and accretion mechanism of extraterrestrial matter accreted on Earth and sheds light on accretion processes and fluxes in the geologic past. The chapters in the first part of the book are arranged in order to follow extraterrestrial matter from its origin in space, its orbital evolution on its way to Earth, its interaction with the Earth magnetosphere and atmosphere to its more or less violent collision with the Earth's surface. In the second part of the book several chapters deal with the present?day flux of cosmic dust and meteorites to Earth. Finally, several chapters deal with the reconstruction of the accretion history of extraterrestrial matter on Earth, starting with the most recent geologic past and ending with the very early, violent accretion period shortly after the formation of Earth, Moon and other solid planets in our solar system.

When in 1981 Louis and Walter Alvarez, the father and son team, unearthed a tell-tale Iridium-rich sedimentary horizon at the 65 million years-old Cretaceous-Tertiary boundary at Gubbio, Italy, their find heralded a paradigm shift in the study of terrestrial evolution. Since the 1980s the discovery and study of asteroid impact ejecta in the oldest well-preserved terrains of Western Australia and South Africa, by Don Lowe, Gary Byerly, Bruce Simonson, Scott Hassler, the author and others, and the documentation of new exposed and buried impact structures in several continents, have led to a resurgence of the idea of the catastrophism theory of Cuvier, previously largely supplanted by the uniformitarian theory of Hutton and Lyell. Several mass extinction of species events are known to have occurred in temporal proximity to large asteroid impacts, global volcanic eruptions and continental splitting. Likely links are observed between asteroid clusters and the 580 Ma acritarch radiation, end-Devonian extinction, end-Triassic extinction and end-Jurassic extinction. New discoveries of 3.5 3.2 Ga-old impact fallout units in South Africa have led Don Lowe and Gary Byerly to propose a protracted prolongation of the Late Heavy Bombardment ( 3.95-3.85 Ga) in the Earth-Moon system. Given the difficulty in identifying asteroid impact ejecta units and buried impact structures, it is likely new discoveries of impact signatures are in store, which would further profoundly alter models of terrestrial evolution..

Due to its specific chemical and physical properties, water is essential for life on Earth. And it is assumed that this would be the case for extraterrestrial life as well. Therefore it is important to investigate where water can be found in the Universe. Although there are places that are completely dry, places where the last rainfall happened probably several 100 million years ago, surprisingly this substance is quite omnipresent. In the outer solar system the large satellites of Jupiter and Saturn are covered by a thick layer of ice that could be hiding a liquid ocean below. This of course brings up the question of whether the recently detected extrasolar planets could have some water on their surfaces and how we can detect this. Water molecules are also found in interstellar gas and dust clouds. This book begins with an introductory chapter reviewing the physical and chemical properties of water. Then it illuminates the apparent connection between water and life. This is followed by chapters dealing with our current knowledge of water in the solar system, followed by a discussion concerning the potential presence and possible detection of water on exoplanets. The signature of water in interstellar space and stars are reviewed before the origin of water in the Universe is finally discussed. The book ends with an appendix on detection methods, satellite missions and astrophysical concepts touched upon in the main parts of the book. The search for water in the Universe is related to the search for extraterrestrial life and is of fundamental importance for astrophysics, astrobiology and other related topics. This book therefore addresses students and researchers in these fields.

Today many scientists recognize plasma as the key element in understanding new observations in interplanetary and interstellar space, in stars, galaxies, and clusters of galaxies, and throughout the observable universe. Plasma astrophysics and cosmology, as a unified discipline, cover topics such as the large scale structure and filamentation of the universe; the microwave background; the formation of galaxies and magnetic fields; active galactic nuclei and quasars; the origin and abundance of light elements; star formation and the evolution of solar systems; redshift periodicities and anomalous redshifts; general relativity; electric fields; the acceleration of charged particles to high energies; and cosmic rays. Plasma Astrophysics and Cosmology is an update on the observations made in radio, optical, and high-energy astrophysics, especially over the last decade, and addresses the paradigm changing discoveries made by the planetary probes and satellites, radio telescopes, and the Hubble space telescope. Over twenty contributors, all distinguished plasma scientists, present an entirely new picture of the nature of our plasma universe with articles ranging from the popular level to advanced topics in plasma cosmology.

Advanced technologies in astronomy at various wavelengths have provided us with high resolution and high quality data on the QSO population. This meeting was aimed at understanding the morphology and nature of the host galaxies and environments of QSOs. The invited lectures as well as the contributed and poster papers highlighted the main issues of current research: the stellar and gaseous content of the underlying galaxy; the characterization of the population of companions and the nature of their interaction with the host galaxy; the connection between radio-loud QSO and radio-galaxies, and QSOs and ULIRGs; the evolution with redshift of both the host galaxy and its environment, and the main implications in theories of galaxy formation and evolution. This volume provides a valuable overview and timely update of the exciting and rapidly developing field of QSO hosts and their environments - essential reading for graduate students and researchers.

In June of 1996, at the idyllic seaside resort of Guaruja, Brazil, a renowned group of researchers in space and astrophysical plasmas met to provide a forum on Advanced Topics on Astrophysical and Space Plasmas at a school consisting of some 60 students and teachers, mainly from Brazil and Argentina, but also from all the other parts of the globe. The purpose was to provide an update on the latest theories, observations, and simulations of space-astrophysical plasma phenomena. The topics covered included space plasma mechanisms for particle acceleration, nonthermal emission in cosmic plasma, magnetohydrodynamic instabilities in solar, interstellar, and other cosmic objects, magnetic field line reconnection and merging, the nonlinear and often chaotic structure of astrophysical plasmas, and the advances in high performance supercomputing resources to replicate the observed phenomena. The lectures were presented by Professor Mark Birkinshaw of the Harvard-Smithsonian Center for Astrophysics and the University of Bristol; Dr Anthony Peratt, Los Alamos National Laboratory Scientific Advisor to the United States Department of Energy; Dr Dieter Biskamp of the Max Planck Institute for Plasma Physics, Garching, Germany; Professor Donald Melrose, Director, Centre for Theoretical Astrophysics, University of Sydney, Australia; Professor Abraham Chian of the National Institute for Space Research, Brazil; and Professor Nelson Fiedler-Ferrara of the University of Sao Paulo, Brazil. As summarized by Professor Reuven Opher, Institute of Astronomy and Geophysics, University of Sao Paulo, the advanced or interested student of space and astrophysical plasmas will find reference to nearly all modern aspects in the field of Plasma Astrophysics and Cosmology in the presented lectures.

Les deuxiernes "Rencontres de l'Observatoire", qui ont eu lieu a l'Observatoire de Paris a Meudon du 10 au 14 Janvier 2000, ont reuni autour du theme "Problernes ernergents en physique de I'espace" 120 physiciens et astrophysiciens venus d'une vingtaine de pays differents. Nous avons voulu honorer a cette occasion Jean-Louis Steinberg pour ses con- tributions majeures a la recherche spatiale, ala radioastronomie et a la physique de I'espace. L'approche explicitement pluridisciplinaire de ce colloque, qui ne s'est pas laisse confiner dans les limites etroites de la physique spatiale ni dans celles imposees par certains programmes officiels, suit l'esprit de sa carriere scientifique: sortir des limites des sujets deja etudies ou sur Ie point de l'etre, et appliquer les connaissances acquises pour explorer de nouveaux domaines. Ce dernier quart de siecle a vu une croissance vertigineuse des performances spatiales. La technologie moderne ne perrnet pas encore de jongler avec les univers comme Ie prestidigitateur de Grandville (Grandville, Un autre monde, ed. H. Four- nier, Paris, 1844); mais quelques decades ont suffi pour voir des instruments soph- istiques explorer les frontieres du systerne solaire, et la cornmunaute de la recher- che spatiale a depasse rapidement Ie sujet etroit de I'environnement soleil-terre pour s'interesser a I'ensemble de l'heliosphere, OU les memes processus physiques sont a I'ceuvre.

My goal in writing this book was to provide an introduction to meteorite science and a handbook on meteorite classification. Insofar as I succeeded it should prove useful both to the practicing professional and to university students at the upper-division and graduate levels. I originally intended the book to be nearly twice as long. The second half was to be a review of properties relating to the origin of each group of meteorites. Chapter XVIII is an example of how these later chapters would have looked, although most would not have been as interpretative. These chapters would have been useful chiefly to meteorite researchers looking for a quick summary of group properties; they were not written because of lack of time. Perhaps I will start to prepare this "second volume" in a year or so when my family and I have recovered from the preparation of the present volume. Although some parts of the classification portion are mildly icono clastic, I have attempted either to avoid the inclusion of speculative interpretations or to flag them with a caveat to the reader. I have relaxed these principles somewhat in Chapter XVIII to conserve space, but even there the discussion of alternative speculations should give the reader a feeling for the degree of uncertainty attached."

Are there other planetary systems like ours? Other planets like ours? Is there life elsewhere in the Universe?' So asks Dr. Lew Allen Jr. in the Foreword. In December of 1992, theorists, observers, and instrument builders gathered at the California Institute of Technology to discuss the search for answers to these questions. The International Conference, entitled Planetary Systems: Formation, Evolution, and Detection' and supported through NASA's newly formed TOPS (Toward Other Planetary Systems) program, was the first of a series of conferences uniting researchers across disciplines and political boundaries to share thoughts and information on planetary systems. The conference was sponsored by NASA, hosted by JPL at Caltech, and endorsed by the 1992 International Space Year Association. These proceedings include discussions of topics ranging from stellar, disk, and planetary formation to new ways of searching for other stellar systems containing planets. The authors represent a wide range of nationalities, disciplines, and points of view. The second international conference took place in December of 1993.

The 19th ESLAB Symposium on 'The Sun and the Heliosphere in Three Dimensions' was held in Les Diablerets (Switzerland) on 4-6 June 1985. Organised almost exactly ten years after the Goddard Space Fl i ght Center Sympos i um dea 1 i ng with the Sun and the i nterp 1 anetary medium in three dimensions, the aim of this Symposium was not only to review the progress made in understanding the three-dimensional structure and dynamics of the heliosphere, but also to look ahead to the scientific return to be expected from the Ulysses mission. Scheduled for launch in May 1986, the scientific instrumentation on board Ulysses will shed light on the conditions and processes occurring away from the ecliptic plane, thereby adding literally a new dimension to our understanding of the only stellar plasmasphere to which we have direct access. The scientific programme of the Symposium was built around a series of invited review papers dealing with aspects of the corona and its influence on the interplanetary medium via transient ejecta, the solar wind, energetic solar particles and galactic cosmic rays, interplanetary dust and neutral gas. These invited talks were supplemented by a number of contributed and poster papers. With the exception of three contributed talks and Wibberenz' review of coronal and acceleration of energetic particles, all papers propagation presented at the Symposium are included in this volume.

In this volume of essays, the top experts and major players behind the United States's recently renewed push to the moon fuel a growing debate over lunar exploration. The announcement in 2004 that the U.S. would be revamping its moon program inspired both excitement about the possibilities and concern over cost and safety issues. This book takes the controversy out of the realm of pure science and into the mainstream of national debate. Lunar experts Alan Binder, Andy Chaikin, Yoji Kondo, Courtney Stadd, Frank White, and many others weigh in on the case for a return, point out the best way to do it, and speculate on what could be done with this newly obtained real estate. The essays are accompanied by illustrations of what life on the moon might look like. Contributions come from different perspectives and styles, offering a broad take on the very real possibility that humans will again walk-- and work, live, and play-- on the lunar landscape. From telescopes and tourism, to training for Mars, to building a new branch of humanity and saving the Earth, this compendium makes the case for sending people back to the moon.

Based on the author s own work and results obtained by international teams he coordinated, this SpringerBrief offers a concise discussion of the origin and early evolution of atmospheres of terrestrial planets during the active phase of their host stars, as well as of the environmental conditions which are necessary in order for planets like the Earth to obtain N_2-rich atmospheres. Possible thermal and non-thermal atmospheric escape processes are discussed in a comparative way between the planets in the Solar System and exoplanets. Lastly, a hypothesis for how to test and study the discussed atmosphere evolution theories using future UV transit observations of terrestrial exoplanets within the orbits of dwarf stars is presented."

The Alexander von Humboldt Colloquium on Celestial Mechanics (sub titled "The Stability of Planetary Systems") was held in Ramsau, Styria, in the Austrian Alps, from March the 25th to the 31st, 1984. The dedication of the meeting to Alexander von Humboldt presented partici pants with the challenge that the discussions during the week should reflect the spirit of that great scientist of the last century, that the very many interesting ideas presented and developed during the sessions should be interpreted in the light of a broad v ew of astron omy and astrophysics. The topics of the meeting ranged from astrometric questions relating to the specification of inertial reference systems, motion of planets (including minor planets) and satellites, with the recurring topic of the search for criteria of stability of the systems, resonances, periodic orbits, and to the origin of the systems. Each session began with one or more invited review papers, followed by offered contributions and discussion. Three evening discussions were held, devoted respectively to inertial systems, to numerical integration techniques, and to cosmogonic problems and ring systems. On the evening of Wednesday, March 28th, a recital of chamber mus c was given by Bernhard Piberauer, on the violin, and Meinhard Prinz, on the piano."

Starting in 1995 numerical modeling of the Earth's dynamo has ourished with remarkable success. Direct numerical simulation of convection-driven MHD- ow in a rotating spherical shell show magnetic elds that resemble the geomagnetic eld in many respects: they are dominated by the axial dipole of approximately the right strength, they show spatial power spectra similar to that of Earth, and the magnetic eld morphology and the temporal var- tion of the eld resembles that of the geomagnetic eld (Christensen and Wicht 2007). Some models show stochastic dipole reversals whose details agree with what has been inferred from paleomagnetic data (Glatzmaier and Roberts 1995; Kutzner and Christensen 2002; Wicht 2005). While these models represent direct numerical simulations of the fundamental MHD equations without parameterized induction effects, they do not match actual pla- tary conditions in a number of respects. Speci cally, they rotate too slowly, are much less turbulent, and use a viscosity and thermal diffusivity that is far too large in comparison to magnetic diffusivity. Because of these discrepancies, the success of geodynamo models may seem surprising. In order to better understand the extent to which the models are applicable to planetary dynamos, scaling laws that relate basic properties of the dynamo to the fundamental control parameters play an important role. In recent years rst attempts have been made to derive such scaling laws from a set of numerical simulations that span the accessible parameter space (Christensen and Tilgner 2004; Christensen and Aubert 2006).

It is this editor's distinct pleasure to offer to the readership the text of the lectures presented at our recent NATO Advanced Study Institute held in Cortina d'Ampezzo, Italy between August 6 and August 17, 1984. The invited lectures are printed in their entirety while the seminar contributions are presented as abstracts. Our Advanced Study Institutes were originated in 1972 and the reader, familiar with periodic phenomena, so important in Celestial Mechanics, will easily establish the fact that this Institute was our fifth one in the series. We dedicated the Institute to the subject of stability which itself is a humbling experience since it encompasses all fields of sciences and it is a basic element of human culture. The many definitions in existence and their practical applications could easily fill another volume. It is known in this field that it is easy to deliver lectures or write papers on stability as long as the definition of stability is carefully avoided. On the other hand, if one selects a definition, he might be criticized for using that definition and not another one. In this volume we carefully defined the specific concept of stability used in every lecture. If the reader wishes to introduce other definitions we feel that he should be entirely free and we encourage him to do so. It is also known that certain sta bility definitions and concepts are more applicable to certain given fields than to others."

On the 6th, 7th' and 8th April 1983, a conference entitled "Magnetism, planetary rotation and convection in the Solar System" was held in the School of Physics at the University of Newcastle upon Tyne. The purpose of the meeting was to celebrate the 60th birthday of Prof. Stanley Keith Runcorn and his, and his students' and associates', several decades of scientific achievement. The social programme, which consisted of excursions in Northumberland and Durham with visits to ancient castles and churches, to Hexham Abbey and Durham Cathedral, and dinners in Newcastle and Durham, was greatly enjoyed by those attending the meeting and by their guests. The success ofthe scientific programme can be judged by this special edition of Geophysical Surveys which is derived mainly from the papers given at the meeting. The story starts in the late 1940s when the question of the origin of the magnetic field of the Earth and such other heavenly bodies as had at that time been discovered as having a magnetic field, was exercising the minds of several scientists; notably P. M. S. Blackett at Manchester, W. M. Elsasser at the University of Pennsylvania and E. C. Bullard at Cambridge. Two alternative mechanisms were proposed. In one the magnetic field was in some way connected with the distributed angular momentum of a rotating body; in the other, electric currents in conducting parts within the body were proposed as the source of magnetic field.

Plant hormone research is the favorite topic of physiologists. Past three decades have witnessed that this subject has received much attention. The inquisitive nature of human mind has pumped much in literature on this subject and this volume is the product of such minds. In the following pages various hormonal-controlled physiological processes like, flowering, seed dormancy and germination, enzyme secretion, senes cence, ion transport, fruit ripening, root growth and development, thig momorphogenesis and tendril thigmonasty have been included. The volume also contains a review paper on 'Growth Regulating Activity of Penicillin in Higher Plants' and has been presented for the first time. The vast contents of each review paper have been written by erudite scholars who have admirably carried out their evangelic task to make the text up TO date. This volume, I am sure, would stimulate the appetite of researchers of peripheral disciplines of botany and agricultural sciences and they will continue to enjoy the fun and adventures of plant hormone research. Save one. my most outstanding debts are due to the rich array of the contributors and other plant physiologists specially to Prof. Thomas Gaspar (Belgium), Prof. E. E. Goldschmidt (Isreal), Prof. H. Greppin (Switzerland), Dr. K. Gurumurti (India), Prof. M. A. Hall (U. K. ), Prof. H. Harada (Japan), Dr. M. Kaminek (Czechoslovakia), Dr. J. L. Karm oker (BangIa Desh), Prof. Peter B. Kaufman (U. S. A. ), Dr. V. I. Kefeli . / (U. S. S. R. ), Dr. M. Kutaoek (Czechoslovakia), Prof. S."

In this volume we compare modem observations of solar flares with results from recent theoretical research and simulation studies on current-carrying loops and their interaction. These topics have undergone rapid developments in the course of recent years. Observational results by X-ray monitoring and imaging spacecraft in the seventies and by dedicated imaging instrumentation in the satellites Solar Max imum Mission and Hinotori, launched 1980 and 1981, have shown the importance of X-ray imaging for understanding the ignition processes of solar flares. Such observations, in tum, stimulated theoretical studies, centered around the flux-tube concept. The classical idea that flares originate by interaction of current-carrying loops was developed and proved to be promising. Concepts on reconnection and coalescence of flux tubes were developed, and their consequences studied. The Yohkoh spacecraft, launched 1991, showed the overwhelming importance of coro nal flux tubes and their many possible ways of interaction. Subsequent and parallel theoretical studies and simulations, differentiating between the topology of interact ing fluxtubes, demonstrated that the mutual positioning and the way of interaction are important for the subsequent processes of energy release in flares and the many associated phenomena such as the expUlsion of jets and the emission of X -ray and microwave radiation. The new developments now enable researchers to understand and classify flares in a physically significant way. Various processes of accelera tion are active in and after flares on greatly varying timescales; these can now be distinguished and explained.

The many papers by Soviet authors have been translated into English by A. P. Kirillov, N. A. Nikiforova, E. A. Voronov, and others. Some of the papers were trans lated by the authors themselves. The discussion records have been prepared at the Institute for Theoretical Astronomy by V. K. Abalakin, N. A. Belyaev, A. P. Kirillov, V. A. Shor, E. A. Voronov, N. S. Yakhontova, and others. The three papers published in French have been carefully checked by B. Milet. The final editing has been done at the Smithsonian Astrophysical Observatory, and we thank J. H. Clark, P. D. Gregory, J. E. Kervick, and G. Warren for retyping much of the material. Our special thanks are due to the D. Reidel Publishing Company for the excellent care they have taken in printing these proceedings of IAU Symposium No. 45. G. A. CHEBOT AREV E. I. KAZIMIRCHAK-POLONSKA Y A B. G. MARSDEN INTRODUCTION The idea to organize a Symposium on 'The Motion, Evolution of Orbits, and Origin of Comets' dates back to the IAU thirteenth General Assembly, held in 1967 in Prague. Owing to the impossibility of completing during the General Assembly the discussion on the problem of orbital evolution of comets Professor G. A. Chebotarev, then the newly elected President of IAU Commission 20, initiated the organization of the international symposium in Leningrad where the full scope of cometary problems might be considered from the viewpoint of celestial mechanics."

At the XV. General Assembly of the International Astronomical Union in Sydney 1973, Commission 10 for Solar Activity requested the incoming Organising Committee to establish a small group to recommend a standard nomenclature for solar features and to prepare an illustrated text which would clear the jungle of terms for the benefit of solar physicists as well as of theoreticians and research workers in related fields. The challenge was taken up by the president of Commission 10, Prof. K. O. Kiepenheuer, and his persuasive advocacy has led eventually to the present book. In the course of the work, the declared aim but not the basic purpose was revised. Rather than prepare a list of standard terms, we have preferred to collect together all the terms that appear in current English-language literature. Synonyms and partially overlapping terms are all recorded for the most part without prejudice. Each has been defined as exactly as possible with the hope that in the future they may be used and understood without ambiguity. It would be a step on the road to standardisation if these terms were not re-used for new phenomena. New observations and new theories will lead to reappraisals and redefinitions so the Glossary is intended more as a guide to the present situation than as a rule-book.