'Fractal geometry addressesitselfto questions that many people have been asking themselves. It con cerns an aspect of Nature that almost everybody had been conscious of, but could not address in a formal fashion. ' 'Fractal geometry seems to be the proper language to describe the complezity of many very compli cated shapes around us. ' (Mandelbrot, 1990a) 'I believe that fractals respond to a profound un easiness in man. ' (Mandelbrot, 1990b) The catchword fractal, ever since it was coined by Mandelbrot (1975) to refer to a class of abstract mathematical objects that were already known at the turn ofthe 19th century, has found an unprecedented resonance both inside and outside the scientific community. Fractal concepts, far more than the concepts of catastrophe theory introduced a few years earlier, are currently being applied not only in the physical sciences, but also in biology and medicine (Goldberger and West 1987). In the mid-eighties, Kadanoff (1986) asked the question: 'Why all the fuss about /ractals' '. He offered a twofold answer: in the first place, it is 'because of the practical, technological importance of fractal objects'. Indeed he emphasised the relevance of these structures for materials scientists and oil drilling engineers, in search of structures with novel properties, or models for the flow of oil through the soil. His second answer was: 'Because of the intellectual interest of fractals '."

The auroral emissions in the upper atmosphere of the polar regions of the Earth are evidence of the capture of energetic particles from the Sun, streaming by the Earth as the solar wind. These auroral emissions, then, are a window to outer space, and can provide us with valuable information about electrodynamic coupling processes between the solar wind and the Earth's ionosphere and upper atmosphere. Studying the physics of these phenomena extends our understanding of our plasma universe.

Ground-based remote-sensing techniques, able to monitor continuously the variations in the signatures of aurorae, in combination with in-situ satellite and rocket measurements, promise to advance dramatically our understanding of the physical processes taking place at the interface of the atmospheres of the Earth and the Sun. Decoding their complexity brings us closer to reliable prediction of communication environments, especially at high latitudes. This understanding, in turn, will help us resolve problems of communication and navigation across polar regions.

Aurorae have been the object of wonder and scientific curiosity for centuries. Only recently, however, have we been able to detect, with sensitive instrumentation, noontime aurorae, and persistent aurorae deep within the polar cap. This book is the first to provide a morphological and theoretical framework for understanding these dayside and polar cap aurorae.

The book also communicates the excitement of discovery, as it details the nature of these newly revealed auroral displays. It is a fascinating voyage of exploration, one appropriate for students of nature, wherever and whoever they may be.

Transitions from the innermost shells of iron, especially the K- and L-shelllines, provide a powerful tool for probing the physical characteristics of hot plasmas in X-ray sources. Their strength and purity allow important conclusions to be drawn even with modest energy resolution. They should also help in studying the regions around black holes and neutron stars. In this book the state of the art and themost recent theoretical and experimental observations are presented. The book will be a valuable source for future satellite missions. It addresses both researchers and graduate students in astrophysics.

This is a fair overview of the basic problems in Solar Physics. The authors address not only the physics that is well understood but also discuss many open questions. The lecturers' involvement in the SOHO mission guarantees a modern and up-to-date analysis of observational data and makes this volume an extremely valuable source for further research.

At this time when astronomers are being surprised by the discovery of objects which emit a fabulously large amount of energy, that is the quasi-stellar radio sources and the quasi-stellar galaxies, and when by the means of space vehicles X rays, gamma rays and cosmic rays are being observed to come from the depths of interstellar space, one may ask why write a book about stars. Stars seem to be almost incidental when one looks at the universe in terms of exceedingly great energies. Nevertheless, stars exist. They are accessible to study and they have not yet revealed all their secrets. This is enough to arouse interest and to cause one to try to find answers to the questions which arise. The early type stars are particularly interesting because they are spendthrift stars pouring out their energy at a great rate. But their brilliance is also their undoing. They must evolve rather quickly, on an astrophysical scale. Thus by studying these stars we are studying a population in change. The implications from the local and from the cosmological viewpoint are important if one wishes to understand the details of stellar evolution and of galactic structure. Perhaps one of the simplest reasons for writing a book about the early type stars is to see if some of the conundrums pre sented by the spectra of these stars can be unravelled when all the available infor mation is brought together."

This volume provides an overview of our current understanding of the physics related to: coronal structures and coronal heating; large-scale coronal shock waves and coronal mass ejections; particle beams in the solar corona and in the interplanetary medium; and explosive energy-release phenomena and particle acceleration. The different articles give a well-balanced presentation of relevant observations based upon various techniques, models and theories, providing a global view of these phenomena and of the underlying physics. In-situ measurements of particles and waves with ULYSSES and WIND and spectral and imaging data from SOHO and YOHKOH provide an unprecedented richness of relevant data. For their better understanding, radio observations - also included in this book - play a key role.

This volume brings together theoretical ideas on the plasma physics of both hot and dense plasmas in the solar atmosphere and similar physics applied to the tenuous and cooler plasmas found in the heliosphere. It is complemented by recent observations. Helioseismology covers the solar interior and the neutrino problem. Solar and stellar activity cycles are addressed. The dynamics of magnetic flux tubes in the solar atmosphere and material flows through the chromosphere into the upper atmosphere are comprehensively reviewed. Energy release processes and the production of energetic particles are important to understanding events in the solar atmosphere and to the dynamics of the tenuous heliosphere. A glimpse of the future is offered by concluding chapters on new ground-based and space instrumentation.

This book contains the proceedings of a workshop held in Schloss Ringberg to assess developments in molecular cloud research over the last 25 years, and to discuss trends for future research in the field of molecular line astronomy. The topics include the morphology, formation, and lifetimes of molecular clouds, and their relation to star formation. Also, the chemical and isotopic content of these clouds is reviewed, and comparisons with molecular clouds in external galaxies are made. This rather complete survey of this important field of research addresses researchers in astronomy and students alike."

This is the first volume of a series on a regular up-to-date coverage of important developments in astronomy and astrophysics jointly published by ESO and Springer-Verlag. Here the reader finds a thorough review of the abundances of the elements up to Boron. Special emphasis is laid on primordial abundances of interest to cosmologists in particular, and on stellar production or destruction respectively. The articles written for researchers and graduate students cover theory and most recent data from telescope observations.

The most luminous compact objects are powered by accretion of mass. Accretion disks are the one common and fundamental element of these sources on widely different scales, ranging from close stellar binaries, galactic black holes and X-ray pulsars to active galactic nuclei (AGN). Key new developments in theory and observations, reviewed by experts in the field, are presented in this book. The contributions to the workshop cover the puzzles presented by the X-UV spectra of AGN and their variability, the recent numerical simulations of magnetic fields in disks, the remarkable behavior of the superluminal source 1915+105 and the "bursting pulsar" 1744-28, to mention a few of the topics.

X-ray astronomy is the prime available window on astrophysical compact objects: black holes, neutron stars and white dwarfs. New observational opportunities have led to an explosion of knowledge in this field. This book provides a comprehensive overview of the astrophysics of compact objects that emit X-rays. Sixteen chapters written by the foremost experts in the field cover the observations and the astrophysical interpretation of these objects. Topics covered include binary systems, gamma ray burst sources, anomalous X-ray pulsars, super-soft sources, and enigmatic fast X-ray transients. Further chapters are dedicated to isolated neutron stars and the X-ray source populations of globular clusters. The properties of X-ray binaries are discussed in depth in chapters on quasi-periodic oscillations and related aperiodic X-ray variability, X-ray bursts, black holes, and relativistic jets. This is a valuable reference for both graduate students and active researchers.

Jean-Pierre Vigier continually labeled one of les heretiques de la science, l'eternel resistant et le patriarche is yet a pillar of modern physics and mathematics, with one leg firmly planted in theory and the other in empiricism spanning a career of nearly 60 years with a publication vitae quickly approaching 400! He wrote of his mentor Louis de Broglie "Great physicists fight great battles", which perhaps applies even more so to 1 Jean-Pierre Vigier himself . If fortune allows a visit to Paris, reported to be the city of love, and certainly one of the most beautiful and interesting cities in the world; one has been treated to a visual and cultural feast. For example a leisurely stroll from the Musee du Louvre along the Champs-Elysees to the Arc de Triomphe would instill even the least creative soul with the entelechies of a poets muse. It is perhaps open to theoretical interpretation, but if causal conditions have allowed one to be a physicist, visiting Paris, one may have taken opportunity to visit the portion of the old Latin quarter in place Jussieu where Pierre et Marie Curie Universite, reported to be 'the best university in France', is stationed.

Helio- and asteroseismology are fast- developing new fields of research that probe the internal structure of stars. The complicated multi-periodic oscillations are studied from both theoretical and observational points of view. Nine articles review the state of the art, including modeling the sun, excitations of oscillations, inverse problems, and the observations of seismic phenomena. One section is devoted to the seismology of stars, a field of research still in its very early development. In addition the reader will find about forty research papers on these subjects.

This book gives a synthesis of the state of the art in artificial intelligence in astronomy and astrophysics, presents its current applications and points out directions of future work. The individual chapters report on the application of artificial intelligence techniques for large astronomical surveys, for processing cosmic ray data, for facilitating data reduction using image processing systems, for telescope scheduling, for observatory ground support operations, for observation proposal preparation assistance, and for scientific applications such as stellar spectral and galaxy morphology classification. The new field of connectionism (neural networks) is also surveyed. The book is designed to be self-contained: a glossary of terms used in this area is provided and an index of terms, acronyms and proper names completes the book.

Leading experts give an overview of very low frequency radio astronomy. They present for the first time in a single conference the astrophysical need for and possible instrumentation for implementing ground-based, ground-to-space, space-based, and lunar-based observations. The papers cover a wide range of topics such as solar astronomy, planetary science, supernova remnants, pulsars, interstellar thermal material, interstellar plasma refraction and diffraction, cosmic rays, extragalactic radio galaxies and quasars, ancient "fossil" radio sources, and new, coherent emission mechanisms.

Satellite observations in various previously unexplored spectral regions have provided a host of data on novae over the last decade. This carefully refereed conference volume is devoted to classical novae and related objects. Around 30 papers discuss observations (basic properties of novae, outbursts, and nebular ejecta), theoretical considerations, and models of observations. In addition the reader will find an introductory review on binary stars by R.P. Kraft and a summary by P. Eggleton of the papers and posters presented at the conference. To help the reader in finding any specific subject or stellar object the volume concludes with a detailed index.

Understanding the formation and evolution of early galaxies is one of the most challenging problems in modern astronomy. In this volume leading specialists describe observations of high and intermediate redshift galaxies as well as the deep survey activities. Further topics include cosmology, and modelling and computer simulations of galaxy formation. Thus the reader will find here a fairly complete picture of the state of the art in this active field of astrophysics research.

It is well known that stellar winds are variable, and the fluctuations are often cyclical in nature. This property seems to be shared by the winds of cool and hot stars, even though their outflows are driven by fundamentally different physical mechanisms. Since very similar models have been proposed to explain the cyclical wind variations observed in a wide variety of stars, the time was ripe for astrophysicists from many different sub-disciplines to present the state of the art in a concise form. The proceedings will provide a useful, up-to-date overview of the observations, interpretation, and modelling of the time-dependent mass outflows from all sorts of stars.

Jets are ubiquitous in the Universe, but ill-understood. Conservative books base their interpretations on focused stellar winds, ejected "bullets," black-hole central engines, and in-situ upgrading of electron energies via shocks. This volume, however, attempts a uniform interpretation of the bipolar-flow family, involving extremely relativistic pair plasma as the jet substance, and rotating magnets (possibly burning disks) as the central engines. Among the discussed sources are SS 433, YSO jets, planetary nebulae, our galactic center, and the class of extragalactic QSOs, both radio-loud and radio-quiet.

This book is based on the Proceedings of the 9th European Workshop on White Dwarfs, the most recent in a series of meetings which have become the most important events in this field. Many of the contributions, however, have been expanded considerably by the authors to include introductory material. This makes this volume a useful, up-to-date introduction into the present status of observations and theory of white dwarf stars.

Jupiter's ice moon Europa is widely regarded as the most likely place to find extraterrestrial life. This book tells the engaging story of Europa, the oceanic moon. It features a large number of stunning images of the ocean moon's surface, clearly displaying the spectacular crack patterns, extensive rifts and ridges, and refrozen pools of exposed water filled with rafts of displaced ice. Coverage also features firsthand accounts of Galileo's mission to Jupiter and its moons. The book tells the rough and tumble inside story of a very human enterprise in science that lead to the discovery of a fantastic new world that might well harbor life.

This book is based on the lecture notes of a one-semester course on black hole astrophysics given by the author and is aimed at advanced undergraduate and graduate students with an interest in astrophysics. The material included goes beyond that found in classic textbooks and presents details on astrophysical manifestations of black holes. In particular, jet physics and detailed accounts of objects like microquasars, active galactic nuclei, gamma-ray bursts, and ultra-luminous X-ray sources are covered, as well as advanced topics like black holes in alternative theories of gravity. The author avoids unnecessary technicalities and to some degree the book is self-contained. The reader will find some basic general relativity tools in Chapter 1. The appendices provide some additional mathematical details that will be useful for further study, and a guide to the bibliography on the subject.

This monograph attempts to provide a systematic and consistent survey of the fundamentals of the theory of free, linear, isentropic oscillations in spherically symmetric, gaseous equilibrium stars, whose structure is affected neither by axial rotation, nor by the tidal action of a companion, nor by a magnetic eld. Three parts can be distinguished. The rst part, consisting of Chaps.1-8, covers the basic concepts and equations, the distinction between spheroidal and toroidal normal modes, the solution of Poisson's differential equation for the perturbation of the gravitational potential, and Hamilton's variational principle. The second part, consisting of Chaps.9-13, is devotedto the possible existenceof waves propagating in the radial direction, the origin and classi cation of normal modes, the comple- ness of the normal modes, and the relation between the local stability with respect to convection and the global stability of a star. In the third part, Chaps.14-18 c- tain asymptoticrepresentationsof normalmodes. Chapter 19 deals with slow period changes in rapidly evolving pulsating stars. The theory is developed within the framework of the Newtonian theory of gr- itation and the hydrodynamics of compressible uids. It is described in its present status, with inclusion of open questions. We give preference to the use of the adjective "isentropic" above that of the adjective "adiabatic," since, from a thermodynamic point of view, these stellar - cillations are described as reversible adiabatic processes and thus as processes that take place at constant entropy.

For almost three decades since Mariner 2 flew by the planet in December 1962, Venus has been the subject of intense investigation by both the Soviet and American space programs. Since the intrinsic magnetic field of Venus is exceedingly weak, if it exists at all, we expect many phenomena of the upper atmosphere and ionosphere of Venus to differ from their terrestrial counterparts. While flybys and landings of the many Venus missions provided useful data on these phenomena, orbital missions were needed for their detailed investigation. Such orbital missions were provided by the Soviet program with Veneras 9 and 10 in October 1975 and by the United States with the Pioneer Venus Orbiter in December 1978. Originally designed for a prime mission of only 243 days, the Pioneer Venus Orbiter is still functioning over a decade later, providing data nearly - hours a day through one of the most active solar cycles to date. We expect these transmis sions to continue until September 1992 when gravitation perturbations will lower the periapsis of the PVO orbit so that the spacecraft will be lost to the atmosphere. The Venera 9 and 10 and the Pioneer Venus observations have led to an explosion of knowledge about the upper atmosphere and ionosphere of Venus and their interaction with the solar wind. The availability of data over a full solar cycle has."

During the past decade, convincing evidence has been accumulated concerning the effect of active galactic nuclei (AGN) activity on the internal and external environment of their host galaxies. Featuring contributions from well-respected researchers in the field, and bringing together work by specialists in both galaxy formation and AGN, this volume addresses a number of key questions about AGN feedback in the context of galaxy formation. The topics covered include downsizing and star-formation time scales in massive elliptical galaxies, the connection between the epochs of supermassive black hole growth and galaxy formation and the question of whether AGN and star formation coexist. Authors also discuss key challenging computational problems, including jet-interstellar/intergalactic medium interactions, and both jet- and merging-induced star formation. Suitable for researchers and graduate students in astrophysics, this volume reflects the engaging and lively discussions taking place in this emerging field of research.