The following text forms the proceedings of a conference. It is supposed to contain what was actually reported and discussed, though it does this, one hopes, in a polished and organized way. A sense of actuality, a reporting quality, makes this book different from a collection of review papers as, for example, a book in the series on Stars and Stellar Systems. All Invited Reports have been included as the Reporters wrote them. The Editor's task has been restricted to improving the presentation, a process which in most cases involved only minor revisions. In a few Reports the Editor did some heavy rewriting; in those cases he checked with the Reporters. Obviously a different course had to be taken with respect to the Discussions. They were recorded on tape, transcribed verbatim and then passed back to the discussants. After the discussants returned their versions, the Editor rearranged and condensed the texts and made a considerable effort to provide references. (Unfortunately he was not able to locate all relevant Russian papers from 1968 and 1969. ) The Editor takes the responsibility for mistakes made in this process, which may have produced occasionally his own 'mix-master Universe'. Actually only a few discussion remarks were rejected, more often because of incomprehensibility, rather than because the remark was far from the subject of the Symposium, or was too long, or was too trivial. A few very long remarks have been condensed and put at the end of a Discussion.

The book aims to present current knowledge concerning the propagation of electro magnetic waves in a homogeneous magnetoplasma for which temperature effects are unimportant. It places roughly equal emphasis on the radio and the . hydromagnetic parts of the electromagnetic spectrum. The dispersion properties of a magnetoplasma are treated as a function both of wave frequency (assumed real) and of ionization density. However, there is little discussion of propagation in a stratified medium, for of collisions is included only which reference may be made to Budden 1] . The effect in so far as this can be done with simplicity. The book describes how pulses are radiated from both small and large antennas embedded in a homogeneous magneto plasma. The power density radiated from a type of dipole antenna is studied as a function of direction of radiation in all bands of wave frequency. Input reactance is not treated, but the dependence of radiation resistance on wave frequency is described for the entire electromagnetic spectrum. Also described is the relation between beaming and guidance for Alfven waves."

The IAU Colloquium No. 59, "The effects of mass loss on Stellar Evolution" was held on September 15-19, 1980 at the International Centre for Theoretical Physics, Miramare, Trieste (Italy), under the auspices of the IAU Executive Co~ mittee and the Italian National Council of Research. The planning of this conference began two years ago du ring the IAU Symposium No. 83 "Mass loss and evolution of 0 type stars" (Qualicum Beach, Victoria, Canada) when we felt that mass loss and its effects on the evolution of stars was too broad a subject for being confined to 0 type stars only. Therefore we thought that a conference dealing with the general problem of mass loss across the whole HR diagram would have been of interest to all people working in the field. The main idea was that bringing together Astronomers and Astrophysicists of the widest range of interests and e~ pertize - all in some way related to the problem of mass loss from stars - would have spurred thorough discussions on the many aspects and implications of this topic. We hope this goal has been achieved. Furthermore, the most recent observational and theoreti cal developments on the problem of mass loss from early ty pe stars avoided this meeting to be a simple updating of the Qualicum Beach Symposium as far as this issue is concerned.

Radio techniques were the nrst to lead astronomy away from the quiescent and limited Universe revealed by traditional observations at optical wave lengths. In the earliest days of radio astronomy, a handful of radio physicists and engineers made one startling discovery after another as they opened up the radio sky. With this collection of classic papers and the extensive intro ductory material, the reader can experience these exciting discoveries, as well as understand the developing techniques and follow the motivations which prompted the various lines of inquiry. For instance he or she will follow in detail the several attempts to detect radio waves from the sun at the turn of the century; the unravelling by Jansky of a "steady hiss type static"; the incredible story of Reber who built a 9 meter dish in his backyard in 1937 and then mapped the Milky Way; the vital discoveries by Hey and colleagues of radio bursts from the Sun and of a discrete source in the constellation of Cygnus; the development of receivers and interferometry in the post-war years by the groups led by Ryle in Cambridge and Pawsey in Sydney; the nrst measurements and exciting identiftcations of Taurus A (the Crab Nebula), Centaurus A, Virgo A, Cassiopeia A, and Cygnus A, the last opening the neld of radio cosmology; the early development of synchroton theory; and the prediction and discovery seven years later of the 21 cm line of neutral hy drogen."

Since 1976 a meeting devoted to recent research on cataclysmic variables ("CV workshop") has been held annually somewhere in North America. Many of the meetings have been held - following a custom older than anyone reading this book - in locations with well-known recreational potential (e. g. Santa Cruz, CA; Boulder, CO). We thought hard about this custom while contemplating the possibility of organi zing a meeting in Massachusetts in the middle of winter. Nobody wants their meeting to go down in history as the smallest and dullest, and it ~ surely be the coldest. But on occasion, meeting organizers have defied custom and scheduled meetings for less~than-trendy places, and gotten away with it (Ur*bana, IL and Rochester, NY must be reckoned as examples of this). Encouraged by the spatial and temporal proximity of the American Astronomical Society meeting (Boston, January 9-12), we thought we might get away with it again, and so came to organize a meeting for January 12-15, 1983, in Cambridge, MA. There was another reason for a meeting at this time and place, we loftily proclaimed in early mailings. No one doubts that the CV's are closely related to the low-mass X-ray binaries ("LMXB' s"), in which the accreting star is usually, or perhaps always, more compact than a white dwarf. Many of the general characteristics of LMXB's sound pretty familiar to any student of CV's: orbital periods in the range 0.

On April 28 1986 Cornelis de Jager reached the age of 65 years. On April 30 he officially retired from the University of Utrecht where he has held a Chair for Stellar Astrophysics, later changed into Space Physics, since 1958. Cees de Jager, as he prefers to be called by his friends, has had an active and successful life in science. His interest in astronomy was raised by his father under the clear skies of Celebes (Indonesia). He started a study in physics and astronomy as a student of the late M. Minnaert in Utrecht during World War II. When in 1943 the occupying forces recruited students who did not want to sign the declaration of loyalty for their war-efforts, Cees and three fellow students went into hiding at the Observatory in Utrecht. During this very "quiet" period van de Hulst developed the theory of the 21 em radiation of neutral hydrogen and de Jager started the observations of variable stars in the pitch dark nights of a country at war. The study of Beta Cepheids rapid ly awoke his interest which was kept throughout the years. In 1958 he organized an international campaign to observe 12 Lac spectroscopically and photometrically, which was a great success."

This volume is the product of Lecturers in the fourth Course of the International School of Cosmic-Ray Astrophysics held at the Ettore Majorana Center in Erice, Sicily in November, 1984. The Course, devoted to "Cosmic Radiation in Contemporary Astrophysics," was concurrently a NATO-sponsored Advanced Study Institute (ASI). Cosmic-ray research is in a state of ferment. Precise measure ments - some made with instruments aboard sattelites and space probe- have been confronting models and theories with severe constraints. The observations of gamma-ray sources, notably Cyg X-3, at energies up to 16 10 eV, have opened up tantalizing possibilities of direct source iden tification. This ASI was devoted largely to interdisciplinary phenomena in cosmic-ray astrophysics whose understanding requires input from the other channels in astronomy. It explored the ways in which progress in cosmic-ray science might clarify phenomena observed in related disciplines. In trying to achieve this aim, we assembled a staff of lecturers representing various astrophysical specialties, such as radio astronomy, optical astronomy, X-ray astronomy, gamma-ray astronomy, and of course, particle astronomy (i.e., cosmic radiation). Students and other participants were likewise drawn from diverse backgrounds. Vigorous discussions enlivened almost every session."

This book represents the Proceedings of the NATO Advanced Study Insti tute on Formation and Evolution of Low Mass Stars held from 21 September to 2 October 1987 at Viana do Castelo, Portugal. Holding the meeting in Portugal recognized both the historical aspects and the bright future of astronomy in Portugal. In the early sixteenth century, the Portugese played an important role in the critical diffusion of classical and medieval knowledge which formed so large a part of scientific activity at that time. Navigation and course setting, brought to a high level by Portugese explorers, relied on mathematics and astronomy to produce precise tables of solar positions. In contemporary Portu gal, astronomy is the focus of renewed interest and support at the universities. It is thus particularly appropriate that the NATO Advanced Study Institute was held on the coast of the Atlantic Ocean in the friendly surroundings of the Costa Verde."

I - PRIMORDIAL NUCLEOSYNTHESIS 1 --. -~-~----,---,-. --------- H. Reeves Primordial nucleosynthesis in 1985 3 The puzzle of lithium in evolved stars H. Reeves 13 High energy particles in dark molecular H. Reeves clouds 23 P. Delbourgo-Salvador, G. Malinie, J. Audouze Standard big bang nucleosynthesis and 3 chemical evolution of D and He 27 G. steigman, D. S. P. Dearborn, D. N. Schramm The survival of Helium,3 in stars 37 G. steigroan How degenerate can we be ? 45 J. Audouze, D. Lindley, J. Silk 3 Early-photoproduction of D and He and pregalactic nucleosynthesis of the light elements 57 R. Schaeffer, P. Delbourgo-Salvador, J. Audouze Influence of quark nuggets on primordial nucleosynthesis 65 T. P. Walker, E. W. Kolb, M. S. Turner Primordi. al nucleosynthesis with generic part. icles 71 D. N. Schramm Dark matter and cosmological nucleosynthesis 79 B. J. Carr Nucleosynthetic consequences of population [II stars W. Glatzel 87 vi CONTENTS 95 I I -EXPWSIVE OBJECTS J. W. Truran Nucleosynthesis accompanying classical nova outbursts 97 M. Wiescher, J. GOrres, P. -K. Thielemann, H. Ritter Reaction rates in the RP-process and nucleosynthesis in novae 105 Type I supernovae ll3 J. C. Wheeler R. canal, J. lsern, J. Labay, R. Lbpez Nucleosynthesis and type I supernovae 121 P. -K. Thielemann, K. Nomoto, K. Yokoi EXplosive nucleosynthesis in carbon deflagration models of type I supernovae 131 E. Mi. iller, Y. Eriquchi Differentially rotating equilibrium models and the collapse of rotating degenerate configurations 143 S. E. WOOsley, T. A.

Recent years have witnessed the expansion and multiplication of the observations of star formation and fragmentation accompanied by a consequent growth in the study of the underlying physical processes, the chemistry, the sites, the times, etc. Moreover, recent studies have shown that the formation of stars is likely to share many features with the formation of other self-gravitating objects. The present volume, therefore, discusses the formation of such objects in a systematic and comparative manner.

Red giant and supergiant stars have long been favorites of professional 6 and amateur astronomers. These enormous stars emit up to 10 times more energy than the Sun and, so, are easy to study. Some of them, specifically the pulsating long-period variables, significantly change their size, brightness, and color within about a year, a time scale of interest to a single human being. Some aspects of the study of red giant stars are similar to the study of pre-main-sequence stars. For example, optical astronomy gives us a tantalizing glimpse of star forming regions but to really investi gate young stars and protostars requires infrared and radio astronomy. The same is true of post-main-sequence stars that are losing mass. Optical astronomers can measure the atomic component of winds from red giant stars that are undergoing mass loss at modest rates 6 (M $ 10- M9/yr.). But to see dust grains and molecules properly, 5 especially in stars with truly large mass loss rates, ~ 10- M9/yr, one requires IR and radio astronomy. As this stage of copious mass loss only lasts for ~105 years one might be tempted to ask, "who cares?".

The 33rd Annual Denver Conference on Applications of X-Ray Analysis was held July 30-August 3. 1984. on the campus of the University of Denver. Following the recent tradition of alternating plenary lecture topics between X-ray diffraction and X-ray fluorescence at the confer ence. the plenary sessions dealt with topics of X-ray fluorescence. Prof. H. Aiginger presented a plenary lect re on TOTAL REFLECTANCE X-RAY SPECTROMETRY which admirably described this relatively new technique. J. C. Russ discussed XRF AND OTHER SURFACE ANALYTICAL TECHNIQUES which gave an excellent overview of the role XRF plays in a modern analytical laboratory. J. E. Taggart. Jr. described THE ROLE OF XRF IN A MODERN GEOCHEMICAL LABORATORY and presented many case histories of the configura tion of analytical equipment in several geochemical laboratories. The plenary lectures demonstrated both the dynamic nature of research in X-ray fluorescence. and the important role X-ray spectrom etry plays in the arsenal of analytical methods found in modern labora tories. Total reflectance X-ray spectrometry takes advantage of con sideration of the geometry of the X-ray optics. Potentially. new sample types may be considered as X-ray fluorescence specimens using this technique."

My interest in the history of the Struve family is long-standing but lay dormant until 1972, when I found myself organizing a symposium of the International Astronomical Union in memory of the second Otto Struve. To satisfy my own curiosity, I investigated the precise relationships of the famous astronomers in the family and published an account of them, based mainly on secondary sources. The exercise made me a ware that there was no biography in English of the first and probably still the greatest astronomer in the clan - Friedrich Georg Wilhelm Struve. Wilhelm's son, the first Otto, wrote an account (in German) of his father's life, intended primarily for family and close friends and --though printed-- not generally available. Through the kindness of a family member I have a copy from which I have been able to work. The Soviet historian of science, Z. K. Sokolovskaya, wrote a biography in Russian, in 1964, to mark the centenary of Wilhelm's death. This had a limited edition, and my efforts to obtain a copy failed. Neither work has, in its entirety, been translated into English, although Michael Meo of Oakland, California, and Kevin Krisciunas of Hilo, Hawaii, have kindly made available to me their unpublished translations of some sections of the latter. In the of a complete copy, however, when I decided to attempt an English absence language biography, I thought it best to do so independently of Sokolovskaya's."

Scientists in the late twentieth century are not the first to view galaxy formation as a phenomenon worthy of explanation in terms of the known laws of physics. Already in 1754 Kant regarded the problem as essentially solved. In his Univerlal Natural Hutory and Theory 0/ the H eaven$ he wrote; "If in the immesurable space in which all the suns of the Milky Way have formed themselves, we assume a point around which, through some cause or other, the first formation of nature out of chaoo began, there the largest mass and a body of extraordinary attraction will have arisen which has thereby become capable of compelling all the systems in the process of being formed within an enormous sphere around it, to fall towards itself as their centre, and to build up a system around it on the great scale . . . . Observation puts this conjecture almost beyond doubt. " More than 200 years later, a similar note of confidence was voiced by Zel'dovicb at an IAU symposium held in Tallin in 1911; "Extrapolating . . . to the next symposium somewhere in the early eighties one can be pretty sure that the question of the formation of galaxies and clusters will be solved in the next few years. " Perhaps few astronomers today would share Kant's near certainty or feel that Zel'dovich's prophecy has been fulfilled, Many, however, will sympathize with the optimistic olltlook of these two statements.

Stellar mass loss is an essential part of the cycling of material from the interstellar medium into stars and back, and must be understood if we are to model processes on galactic to cosmological scales. The study of stellar winds and the effects of stellar mass loss has reached a particularly exciting stage where observational capabilities are increasingly able to provide interesting constraints on models and theories. Recent resu1ts from theoretical and observational work for both hot and cool stars with substantial winds have led to the suggestion that a combination of pulsation with other mechanisms makes for particularly efficient mass loss from stars. This provided the original motivation for the organization of this workshop. The conference was organized along relatively conventional lines according to the types of objects being scrutinized. However the true unity of the proceedings comes from the interplay of the mechanisms involved. For example, for the cool, luminous Mira variables, pulsation leads to shock waves that extend the atmosphere, enhancing dust formation; radiation pressure on dust drives the wind, cooling the atmosphere and in some cases suppressing the shocks. Similarly for the Be stars, both pulsation (in this case, non-radial) and radiation pressure (due to UV resonance lines) are expected to be important, and this expectation is at least qualitatively borne out by the observations.

Over the last decade we have witnessed a rapid change in our understanding of the late stages of stellar evolution. A major stimulus to this has been the synthesis of observational data from different wavebands of the electromagnetic spectrum. The advent of infrared astronomy has led to the discovery of many luminous. late-type stars obscured by their circumstellar dust envelope. Sources discovered in the IRC and AFGL infrared sky surveys were followed up by radio observa tions, leading to the widespread use of the OH and CO molecules as probes of the circumstellar envelopes. Advances in the technique of aperture synthesis have made possible observations with unprecedent resolving power, both in spectral-line and continuum. The success of the recent IRAS sky survey, with the detection of over 250,000 sources, brings the promise of even more exciting years ahead. This area of astronomical research is also blessed with the close collaboration between theorists and observers. New ideas are constantly being quantitatively tested by new data. Theoretical predictions are eagerly used as guides for further observations. This conference was initiated with the following objective: bring together workers in optical, infrared, radio and theoretical astronomy and let them confront each other. Based on the post-conference res ponses we received, many of the participants have indeed found this Workshop a stimulating experience. The Workshop on the Late Stages of Stellar Evolution was held from 2-5 June 1986 in Calgary, Canada."

Within the framework of Ispra Courses, a course on "Applications of Remote Sensing to Agrometeorology" was held from April 6th to 10th, 1987 at the Joint Research Centre of the European Communities, Ispra Italy. The purpose of the course was to familiarize scientists, active in Agrometeorology and related fields, with remote sensing techniques and their potential applications in their respective disciplines. Conventional ground investigations in various fields of natural sciences such as hydrology, pedology and agrometeorology can be supple mented by a range of instruments carried by airborne or earth orbiting platforms. The last few years, in particular, have seen many developments in this respect and a growing amount of information can now be derived not only from dedicated earth resources satellites such as the LANDSAT and SPOT, but also from other platforms such as METEOSAT and the series of NOAA-TIROS. Future platforms (ERS-l, Space Station, etc.) with their advanced sensors will further broaden the range of applications open to the investigators. The use of these data sources, together with field investigations, can lead, at a reduced cost, to a better characterization of the spatial and temporal properties of natural systems."

Peter P. Eggleton and James E. Pringle Institute of Astronomy Madingley Road Cambridge England The 1970's can be described, in retrospect, as the "Decade of the Close Binary." Exciting observations with new technology, combined with classical work, both observational and theoretical, convinced the astronomical world that binary interaction of various kinds is not only interesting but common. Indeed, by 1975 almost anything unusual had a good chance of being interpreted as due to binary interaction. But astronomers are seldom overwhelmed by speculation, even their own, and solid observational work has confirmed or refuted such speculation, without regard to its plausibility. For instance, binarity has been found where it was perhaps least expected, in Barium stars, and refuted where it could most reasonably be expected, in Wolf-Rayets. Unfortunately, many other classes of potential binaries remain without the clearest evidence of binarity, for instance Be stars, symbiotics and blue stragglers. This Advanced Study Institute was held to commemorate John Whelan (1945-1981), whose scientific career, sadly cut short in its prime, did much to further the careful study, theoretical and observational, of close binaries, as well as to encourage the spirit of international friendship and collaboration. His own interests covered a greater field, but "Interacting Binaries" seemed a reasonable restriction. We publish here 15 review talks, which still do not cover the whole topic, although they range widely.

The reader will find in this volume the Proceedings of the NATO Advanced Study Institute held in Cortina d'Ampezzo, Italy between August 3 and August 13, 1987 under the title "Long Term Dynamical Behaviour of Natural and Artificial N-body Systems." The Institute was the latest in a series held in 1972, 1975, 1978, 1981, 1984 in dynamical astronomy, theoretical mechanics and celestial mechanics under the Directorship of Professor Victor Szebehely. These previous institutes, held in high esteem by the international community of research workers, have resulted in a series of well-received and valuable Proceedings. In correspondence with Professor Szebehely and in long discussions with him in Colorado in August 1985, I agreed to his request that I undertake the preparation of a new ASI. I was happy to do so knowing I could call upon his vast experience in overseeing such ASI's. The last quarter century has been a period in which increasingly rapid progress has been made in celestial mechanics and related subjects not only because of the appearance of new problems urgently requiring solution but also because of the advent of new analytical techniques and powerful computer hardware and software.

This volume is the documentation of the first Course on 'Neutron Stars, Active Galactic Nuclei and Jets', of an Erice School with a wide astro physical scope. The choice of the subject was made because of an apparent similari ty - stressed already at earlier meetings - of four classes of astrophy sical jet sources: Active Galactic Nuclei, Young Stellar Objects, Binary Neutron Stars and Binary White Dwarfs. They share important properties such as their morphology, high variability and large veloci ty gradients as well as - with some inference - their broad spectrum, hypersonic outflow and core/lobe power ratio. Despite this apparent similarity of the four source classes, quite different models have been put forward for their description: (i) The central engine of active galactic nuclei has been generally thought to be a black hole, in contrast to the central engine of young stellar objects and cometary nebulae which apparently is a pre-T-Tauri star, some six orders of magnitude less compact, and to the central engine of planetary nebulae which mayor may not be a binary white dwarf. (ii) The elongated lobes, or flow patterns, have been often interpreted as highly directional stellar wind outflows whereas in a few well mapped cases, the elongated flow appears to be 'pumped up' through a much narrower channel, or jet, both in the extragalactic and stellar sources.

Dear Reader, Here is your book. Take it, run with it, pass it, punt it, enjoy all the many things that you can do with it, but-above all-read it. Like all textbooks, it was written to help you increase your knowledge; unlike all too many textbooks that you have bought, it will be fun to read. A preface usually tells of the author's reasons for writing the book and the author's goals for the reader, followed by a swarm of other important matters that must be attended to yet fit nowhere else in the book. I am fortunate in being able to include an insightful prepublication review that goes directly to my motivations and goals. (Look for it following this preface.) That leaves only those other important matters. In preparing the text, I consulted a number of books, chief of which included these: * S. Chandrasekhar, Ellipsoidal Figures of Equilibrium, Yale Uni versity Press, 1969. * J .M.A. Danby, Fundamentals of Celestial Mechanics, Macmil lan, 1962. Now available in a 2nd edition, 3rd printing, revised, corrected and enlarged, Willmann-Bell, 1992. * Y. Hagihara, Theories of Equilibrium Figures of a Rotating Ho mogeneous Fluid Mass, NASA, 1970. * R.A. Lyttleton, The Stability of Rotating Liquid Masses, C- ix x PREFACE bridge University Press, 1953. * C.B. Officer, Introduction to Theoretical Geophysics, Springer Verlag, 1974. * A.S. Ramsey, Newtonian Attraction, Cambridge University Press, 1949. * W.M. Smart, Celestial Mechanics, Longmans, Green, and Co, 1953.

This book is the proceedings of a workshop on stellar continuum radio astronomy that was held in BoUlder, Colorado on August 8-10, 1984. Although it was originally intended to be a small workshop with participants mainly from North America, it evolved to a workshop with 72 partiCipants from twelve countries (U.S.A. 52, Canada 3, the Netherlands 3, United Kingdom 3, Australia 2, Ireland 2, Italy 2, France 1, Mexico 1, Switzerland 1, West Germany 1, and U.S.S.R. 1). This workshop was sponsored by the Joint Institute of Laboratory Astrophysics (JILA) and the University of Colorado. In order to preserve a workshop atmosphere, while still presenting both extensive reviews and contributed papers, an experimental format was adopted. All contributed papers related to the topiCS of the day were presented in poster form in the early morning and were accessible all day. During each morning (or afternoon) session review papers were presented, followed by a coffee break in the poster area adjacent to the conference room. Then the review papers and contributed papers were discussed for roughly one and a half hours. The last session was devoted to invited panel papers and discussion of current and future problems in the field of stellar radio astronomy.

A small country builds a world-class telescope in its backyard and lives happily ever after (or at least for a quarter century). That in a nutshell is the story told in this collection of essays. The country of course is the Netherlands, and the telescope is the Westerbork Synthesis Radio Tele scope (WSRT), brainchild of Jan Oort. Living happily in this context is a continuing record of discovery and as such also a continuing basis for se curing observing time on facilities in other countries and operating at other frequencies. As our community celebrates the Silver Anniversary of the radio tele scope at Westerbork, it is fitting that we pause to take account of the scientific discoveries and insights it made possible. Initially the instrument represented the very significant step away from university-run, specialist facilities to a well-supported, common-user radio imager also having spec tral and polarization capabilities. It pioneered the mode of operation now common for satellite observatories, in which data is taken and calibrated by technicians and provided to researchers ready for analysis. It has been a major source of discovery in, among other areas, research on neutral hy drogen and studies of dark matter in galaxies.

For every astronomical topic that I have approached there has turned out to be a broader realm of possibilities than is commonly accepted or acknowledged. The "excursions" of this book are the examples. They mostly depart from the mainstream of conventional wisdom to offer a wider perspective with opportunities for further research. While my intent is to supplement that mainstream, the effect may appear to dismiss rather than to reconsider accepted tenets. Ample praise and credit for those accomplishments are already available in textbooks. Readers may very well disagree with some of the notions presented in these excursions, but I hope that they will pause long enough to evaluate the scientific basis for any disagreement. For the most part, these excursions remain incomplete and unfulfilled, yet they contain many ideas that are not available elsewhere. Whether these ideas are per ceived as a collection of unproven claims or as a storehouse of fresh opportunities will depend entirely on the attitude of the reader. The excursions do cover a rather wide span of disciplines, and that may lead to an unfocused overall impression. My hope is thereby to attract a broader audience than that of a single discipline, and to expose them to neighboring disciplines. The excursions all do have the common thread of optical science related to astronomy."

For millennia mankind has watched as the heavens move in their stately progression from night to night and from year to year, presaging with their changes the changing seasons. The sun, the moon, and the planets move in what appears to be an unchanging firmament, except occasionally when a new "star" appears. Among the new stars there are comets, novae, and finally supernovae, the subject of this book. Superstitious mankind regarded these events as significant portents and recorded them carefully so that we have records of supernovae that may reach back as far as 1300 B. C. (Clark and Stephenson, 1977; Murdin and Murdin, 1985). The Cygnus Loop, believed to be a 15,000-year-old supernova remnant at a distance of only 800 pc (Chevalier and Seward, 1988), must have awed our ancestors. Tycho's supernova of 1572, at a distance of 2500 pc, had a magnitude of -4. 0, comparable to Venus at its brightest, and Kepler's supernova of 1604 had a magnitude of - 3 or so. Thus the Cygnus Loop supernova might have had a magnitude of - 6 or so, and should have been readily visible in daytime. A supernova in Vela, about 8000 B. C. was comparably close, as was SN 1006, whose magnitude may have been -9. While most of the supernova records come from the Old World, the supernova of 1054 is recorded in at least one petroglyph in the American West.