L\Srrronomy Al TD ASTRC)PIIYSICS I IBRARY

$L\Srrronomy Al TD ASTRC)PIIYSICS I IBRARY$ L\srrRONOMY Al TD ASTRC)PIIYSICS I IBRARY Series Editors: I. Appenzeller, Heidelberg, Gerrnany G. Börner, Garehing, Gerrnany M. Harwit, Washington, DC, USA R. Kippenhahn, Göttingen, Gerrnany J. Lequeux, Paris, France P. A. Strittmatter, Tueson, AZ, USA V. Trimble, College Park, MD, and Irvine, CA, USA ONLINE LlBRARY Physics and Astronomy http://www.springer.de/phys/ Springer-Verlag Berlin Heidelberg GmbH STRC) ():v1Y ANI) A I ROPf YSICS LfBRARY Series Editors: I. Appenzeller . G. Bömer . M. Harwit . R. Kippenhahn 1. Lequeux . P. A. Strittmatter . V. Trimble Stellar Physics (2 volumes) Galaxy Formation By M. S. Longair Volume I: Fundamental Concepts and Stellar Equilibrium Tools of Radio Astronomy 3rd Edition Volume 2: Stellar Evolution and Stability By K. Rohlfs and T. L. Wilson By G. S. Bisnovatyi-Kogan Tools of Radio Astronomy Theory of Orbits (2 volumes) Problems and Solutions Volume 1: Integrable Systems By T. L. Wilson and S. Hüttemeister and Non-perturbative Methods Atoms in Strong Magnetic Fields Volume 2: Perturbative Quantum Mechanical Treatment and Geometrical Methods and Applications in Astrophysics By D. Boccaletti and G. Pucacco and Quantum Chaos The Solar System 2nd Edition By H. Ruder, G. Wunner, H. Herold By T. Encrenaz and J.-P. Bibring and F. Geyer Physics of Planetary Rings The Stars Celestial Mechanics of Continuous Media By E. L. Schatzman and F. Praderie By A. M. Fridman, N. N. Gorkavyi Cosmic Ray Astrophysics The Physics and Dynamics By R. Schlickeiser ofPlanetary Nebulae By G.A. Gurzadyan Gravitational Lenses Astrophysical Concepts 2nd Edition By P. Schneider, J. Ehlers and E. E. Falco ByM. Harwit Relativity in Astrometry, Celestial Stellar Structure and Evolution Mechanics and Geodesy By M. H. Soffel By R. Kippenhahn and A. Weigert The Sun An Introduction By M. Stix Modern Astrometry By J. Kovalevsky Reflecting Telescope Optics (2 volumes) Astrophysical Formulae 3rd Edition Volume I: Basic Design Theory (2 volumes) and its Historical Development Volume I: Radiation, Gas Processes Volume II: Manufacture, Testing, Alignment, and High Energy Astrophysics Modern Techniques Volume II: Space, Time, Matter By R. N. Wilson and Cosmology Astrometry of Fundamental Catalogues By K.R. Lang The Evolution from Optical to Radio The Sun from Space By K. R. Lang Reference Frames By H. G. Walter and O. J. Sovers Observational Astrophysics 2nd Edition By P. Una, F. Lebrun and F. Mignard For more titles see series homepage - http://www.springer.de/phys/books/aal Kenneth R. Lang The SUll from Space With 96 Figures Including 46 Color Figures and 32 Tables Springer Professor Kenneth R. Lang Department of Physics and Astronomy Robinson Hall Tufts University Medford, MA 02155, USA Cover picture: X-ray View of the Solar Cycle. A montage of images from the Soft X-ray Telescope (SXT) aboard Yokhoh showing dramatic changes in the corona as the Sun's II-year magnetic activity cycle changed from maximum to minimum. The 12 images are spaced at 120-day intervals from the time of the satellite's launch in August 1991, at the maximum phase of the II-year sunspot cyde (left), to late 1995 near the minimum phase (right); see Fig. 7.12 on page 235. (Courtesy of Gregory L. Slater and Gary A. Linford, NASA, ISAS, the Lockheed-Martin Solar and Astrophysics Laboratory, the National Astronomical Observatory of Japan, and the University ofTokyo) Library of Congress Cataloging-in-Publication Data. Lang, Kenneth R. The sun from space! Kenneth R. Lang. p. cm. - (Astronomy and astrophysics library). Indudes bibliographical references and index. I. Sun. 2. Astronautics in astronomy. I. Title. 11. Series. QB521.L25 2000 523.7-dc21 00-041038 ISSN 0941-7834 ISBN 978-3-662-04282-3 ISBN 978-3-662-04280-9 (eBook) DOI 10.1007/978-3-662-04280-9 This wark is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on mi crofilm or in any other way, and storage in data banks. Duplication of this publication ar parts thereof is permitted only under the provisions of the Gerrnan Copyright Law of September 9, 1965, in its current version, and permission far use must always be obtained from Springer-Verlag. Violations are liable for prosecution under the Gerrnan Copyright Law. © Springer-Verlag Berlin Heidelberg 2000 OriginaIly published by Springer-Verlag Berlin Heidelberg New York in 2000. Softcover reprint ofthe hardcover 1st edition 2000 The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free far general use. Typeseuing: Data conversion by LE-TeX, Leipzig Cover design: design & production GmbH, Heidelberg Printed on acid-free paper SPIN: 10717748 55!31411ba - 5 432 I 0 This book is dedicated to everyone who is curious, imaginative and intelligent, thereby strengthening the human spirit. Preface Our familiar, but often inscrutable, star exhibits a variety of enigmatic phe nomena that have continued to defy explanation. Our book begins with abrief account of these unsolved mysteries. Scientists could not, for example, under stand how the Sun's intense magnetism is concentrated into dark sunspots that are as large as the Earth and thousands of times more magnetic. Nor did they know exact1y how the magnetic fields are generated within the Sun, for no one could look inside it. Another long-standing mystery is the million-degree solar atmosphere, or corona, that lies just above the cooler, visible solar disk, or photosphere. Reat should not emanate from a cold object to a hotter one anymore than water should flow up hill. Researchers have hunted for the elusive coronal heating mechanism for more than half a century. The Sun's hot and stormy atmosphere is continuously expanding in all di rections, creating a relentless solar wind that seems to blow forever. The exact sources of aB the wind's components, and the mechanisms of its acceleration to supersonic velocities, also remained perplexing problems. The relatively calm solar atmosphere can be violently disrupted by power ful explosions, filling the solar system with radio waves, X-rays, and gamma rays, and hurling charged particles out into space at nearly the speed of light. Other solar explosions, called Coronal Mass Ejections, throw billions of tons of coronal gases into interplanetary space, creating powerful gusts in the solar wind. Yet, we have only just begun to understand the detailed causes of the Sun's explosive outbursts, and no one has been able to predict exact1y when they will occur. In less than a decade, three pioneering spacecraft, named the SOlar and Reliospheric Observatory, or SORO for short, Ulysses and Yohkoh, have transformed our perception of the Sun. They are also described in the intro ductory chapter, together with their principal scientific goals. This scientific troika has examined the Sun with exquisitely sensitive and precise instruments that have widened our range of perception, giving us the eyes to see the invis ible and the hands to touch what cannot be feIt. They have extended our gaze from the visible solar disk, down to the hidden core of the Sun and out in all directions through the Sun's tenuous, expanding atmosphere. SORO, Ulysses and Yohkoh have together provided insights that are vastly more focused and detailed than those of previous solar missions, providing clues to many of the crucial, unsolved problems in our understanding of the Sun. Scientific discoveries are usually not isolated "eureka" moments, occur ring in amental or experiential vacuum. They are built upon a foundation of previous investigations and extrapolated into the future. Our recent accom- VIII Preface plishments in solar physics are the culmination of a long history of prior research, from the earliest optical and radio telescopes to rockets and then full-fledged spacecraft such as Skylab, Helios 1 and 2, and the Solar Max imum Mission. The second chapter of our book describes the discovery of space, provid ing the historical framework needed to understand subsequent results. Here we also introduce ideas and terms that have become so common to our space-age vocabulary that even many practicing scientists have forgotten their origin and meaning. As mentioned in Chap.2, just half a century aga most people visualized out planet as a solitary sphere traveling in a cold, dark vacuum around the Sun. Inquisitive spacecraft have now shown that the space outside the Earth's atmosphere is not empty, and demonstrated that the Earth and other planets are immersed within an eternal, stormy wind. The solar wind is mainly com posed of electrons and protons, set free from hydrogen atoms, the most abun dant element in the Sun, but it also contains heavier ions and a magnetic field. The second chapter also describes the discovery that intense magnetism pervades the Sun's atmosphere, creating an ll-year variation in the level of explosive solar activity, as weIl as the amount of cosmic rays reaching the Earth from the space outside our solar system. X-ray photographs from rock ets and the Skylab space station demonstrated that the Sun's magnetic fields mold and constrain the million-degree gases found in the low solar atmo sphere. Long-Iasting coronal holes, without any detectable X-ray radiation in Skylab's photographs, were also compared with other spacecraft measure ments to show that these places expel a high-speed solar wind. Contextual and historical preludes are also woven into the texture of sub sequent chapters, and usually presented in chronological order. Every chapter, except the first, contains a concluding time-line table that highlights key events and discoveries in the area under consideration.

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