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Double and multiple stars are the rule in the stellar population, and single stars the minority, as the abundance of binary systems in the space surrounding the sun shows beyond doubt.

As a star, the sun is continuously emitting an enormous amount of energy 33 into space, up to as much as 3. 9 X 10 erg/ s. This energy emission consists of three modes. Almost all the energy is emitted in the form of the familiar black-body radiation, commonly called sunlight. Although the amount of energy emitted is small, the sun also emits x rays, extreme ultraviolet (EUV), and UV radiations, which are absorbed above the earth's stratosphere. These constitute the second mode of solar energy, separate from the black-body radiation that penetrates the lower layers of the atmosphere. The sun has another important mode of energy emission in which the energy is carried out by charged particles. These particles have a very wide range of energies, from less than I keY to more than I GeV. Because of this wide range, it is convenient to group them into two components: particles with energies greater than 10 keY and the lower-energy particles. The former are generally referred to as solar protons or solar cosmic rays; their emission is associated with active features on the sun. Their interaction with the atmosphere is similar to that of the x ray and EUV radiation. Low-energy particles constitute plasma, a gas of equal numbers of positive and negative particles. Actually, this plasma is the outermost part of the solar atmosphere, namely the corona, which blows out continuously . For this reason, the plasma flow is called the solar wind.

The usual book on the theory of spectral line formation begins with an in-depth dis­ cussion of radiation transfer, including the elegant methods of obtaining analytical solutions for special cases, and of the physics of line broadening. Neither of those features will be found in this book. It is assumed that the reader is already familiar with the essentials of transport theory and of line broadening and is ready to investi­ gate some of the particular applications of the theory to the flow of line photons through the outer layers of a star, or other tenuous media. The main thrust of this book is toward the compilation and presentation of a vast quantity of computational material available to the author in the form of computer output. The material presented represents a highly filtered sample of the published work in this subject plus an extensive set of previously unpublished results. To present large quantities of computer output in an intelligible and efficient way is a difficult task, for which I have found no really satisfactory solution. Chapters III and IV, in particular, contain almost exclusively this type of presentation. The reader may find these chapters somewhat tedious because of the level of condensation of the material. I have tried to reach a reasonable balance between over condensation and excessive detail, which in the long run may be irrelevant.

This volume, together with its two companion volumes, originated in a study commis sioned by the United States National Academy of Sciences on behalf of the National Aeronautics and Space Administration. In proved necessary to divide the chapters into three separate volumes that cover three different aspects of solar physics.

The data thus obtained on the principal ionizing agent - short-wave solar radiation - and on the physical conditions prevailing in the upper atmosphere and in the ionosphere at different altitudes, allow the proposal of a self-consistent mechanism of ionosphere formation.

This volume, together with its two companion volumes, originated in a study commis sioned by the United States National Academy of Sciences on behalf of the National Aeronautics and Space Administration. This volume is devoted to 'The Solar Interior', except that the volume begins with one chapter reviewing the contents of all three volumes.

No part of the Hertzsprung-Russell diagram shows a more pronounced diversity of stellar types than the upper part, which contains the most luminous stars.

It was expected that theoretical interpretations would be extensively developed in the second part, prepared by de Feiter. Only in Chapter II, concerning the 'low-temperature' flare, do we go deeper into the theoretical interpretations, anticipating that de Feiter would have been concerned mainly with the 'high-energy' physics.

The interaction of prominences with other manifestations of solar activity is the subject of Chapter VI, and the final Chapter VII considers prominences in the larger context: as an integral part of the corona.

The aim of the present book will be to summarize the results of the space exploration of the Moon in the past fifteen years -culminating in the manned Apollo missions of 1969-1972 -on the background of our previous acquaintance with our satellite made in the past by astronomical observations at a distance.

The usual book on the theory of spectral line formation begins with an in-depth dis cussion of radiation transfer, including the elegant methods of obtaining analytical solutions for special cases, and of the physics of line broadening.

Aims to be a balance between theory and applications, of analysis and synthesis, keeping the focus on the comprehension of the physics ruling our planetary system. This work is a textbook for students and a fundamental reference for researchers in the Solar System field.

The purpose of this textbook is to provide a basic knowledge of the main parts of modern astrophysics for all those starting their studies in this field at the undergraduate level. Thus, the primary audience for this work is composed of students in astronomy, physics, mathematics, physical chemistry and engineering.

Short History of Solar Radio Astronomy Since its birth in the forties of our century, solar radio astronomy has grown into an extensive scientific branch comprising a number of quite different topics covering technical sciences, astrophysics, plasma physics, solar-terrestrial physics, and other disciplines.

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.

This volume, together with its two companion volumes, originated in a study commis sioned by the United States National Academy of Sciences on behalf of the National Aeronautics and Space Administration. This volume is devoted to 'The Solar Interior', except that the volume begins with one chapter reviewing the contents of all three volumes.

In September 1984 a Summer School on Solar System Plasmas was held at Imperial College with the support of the Science and Engineering Research Council. Traditionally, different areas of solar system science, such as solar and magnetospheric physics, have been studied by separate communities with little contact.

Our investigations have also been strongly supported by work at other institu tions, especially by a group at the Royal Institute of Technology, Stockholm, where a number of plasma experiments have been made in order to clarify basic processes which are relevant to cosmogonic problems.

Reidel Publishing Company, Dordrecht, Holland No part of this book may be reproduced in any form, by print, photoprint, microfilm, or any other means, without written permission from the publisher TABLE OF CONTENTS PREFACE IX PREFACE BY THE TRANSLATOR XI CHAPTER 1 / THE EARTH AS A CHEMICAL SYSTEM 1 1. The Earth within the Solar System 1 1.

The rather excessive public preoccupation of the immediate past with what has been labeled the 'environmental crisis' is now fortunately being replaced by a more sus tained and rational concern with pollution problems by public administrators, engineers, and scientists.

This book, which was written by the current leaders in the field of Ras research, provides the readers with the most comprehensive and up-to-date view of the major oncogene Ras. This volume is valuable not only for university students in molecular biology, biochemistry or medicine, but also for senior scientists currently conducting cancer research.

In September 1984 a Summer School on Solar System Plasmas was held at Imperial College with the support of the Science and Engineering Research Council. Traditionally, different areas of solar system science, such as solar and magnetospheric physics, have been studied by separate communities with little contact.

Over the past two decades auroral science has developed from a somewhat mysterious and imprecise specialty into a discipline central in the study of the ionosphere and magnetosphere. Generally I have attempted to provide a coherent introduction to auroral science with an emphasis on relatively simple physical interpretations and models.

Stellar physics itself is benefiting greatly from solar discoveries, but, in tum, our understanding of many solar phenomena (such as sunspots, sunspot cycles, the corona and the solar wind) will undoubtedly increase in the future due to their observation under different conditions in other stars.

Only a few positive experimental results have been reported, in spite of an expenditure of considerable effort by many people: in particular, the possible Galactic Center emission line (473 to 530keV) and 'Y-ray lines at several energies (e.