Our conference - opening today - has two aims in view: first, to commemorate some milestones in the development of the studies of close binary systems whose anniversaries fall in these years, as well as to take stock of our present knowledge accumulated through out preceding decades, in order to consider where do we go from here. This summer, 310 years will have elapsed since the first ec lipsing binary - Algol - was discovered in Bologna by Geminiano Montanari (1633-1687) to be a variable star; and 198 years have gone by since John Goodricke of York (1764-1786) established the fact that Algol's light changes were periodic. Moreover, it is al most exactly (to a month) now 100 years since Edward Charles Pickering (1846-1919) of Harvard Observatory in the United States took the first steps towards the development of systematic methods of analysis of the light changes of Algol and related systems - a topic which will constitute the major part of the programme of our present conference. The three dates recalled above illustrate that the discoverers of such celestial objects and observers of their light changes have been systematically ahead of the theoreticians endea vouring to understand the significance of the observed data by de cades and centuries in the past - a fact which, incidentally, con tinues to hold good (albeit with a diminishing lead-time) up to the present."

Proceedings of the 97th Colloquium of the International Astronomical Union, held in Brussels, Belgium, June 8-13, 1987

The words of this preface were written when the book was ready to go to the press; and are limited to only a few points which are best made in this place. As is intimated by the sub-title, the whole volume was written with appli cations in mind to double-star astronomy. The latter is, however, not the only branch of our science which could benefit from its contents. The same is true of certain aspects of the dynamics of stellar systems or galaxies (the stellar popula tions of which are also characterized by the fact that the mean-free-path of their constituent stars are long in comparison with the dimensions of the respective systems); the central condensations of which are high enough to approximate the gravitational action of a "mass-point." This fact did not, to be sure, escape the attention of previous investigators (in the case of globular clusters, in particular, the Roche model was introduced in their studies under the guise of polytropic models characterized by the index n = 5); though no particular attention will be paid to these in this book. But possible applications of the Roche model are not limited to problems arising in stellar astrophysics. With Coulomb forces replacing gravitation, the equilibrium model finds a close analogy in the field of electrostatics-as was pointed out already at the beginning of this century by (then young) J. H. Jeans (cf."

Eclipsing Variables - What They can Tell Us and What We can do with Them The aim of the present book will be to provide an introduction to the inter pretation of the observed light changes of eclipsing binary stars and their analysis for the elements of the respective systems. Whenever we study the properties of any celestial body - be it a planet or a star - all information we wish to gain can reach us through two different channels: their gravitational attraction, and their light. Gravitational interaction between our Earth and its celestial neighbours is, however, measurable only at distances of the order of the dimensions of our solar system; and the only means of communication with the realm of the stars are their nimble-footed photons reaching us - with appropriate time-lag - across the intervening gaps of space. As long as a star is single and emits constant light, it does not constitute a very revealing source of information. A spectrometry of its light can disclose, to be sure, the temperature (colour, or ionization) of the star's semi-transparent outer layers, their chemical composition, and prevalent pressure (through Stark effect) or magnetic field (Zeeman effect), it can disclose even some information about its absolute luminosity or rate of spin. It cannot, however, tell us anything about what we should like to know most - namely, the mass or size (i.e., density) of the respective configuration; its absolute dimensions, or its internal structure."

The twentieth century has been a remarkable epoch in the affairs of men, and this is no less true of astronomy, at once the oldest and most modern of the sciences. Sky watchers at the beginning of the century measured positions and predicted celestial motions in faithful but uninspired homage to the Muse Urania; nowadays, their descendents call on all the resources of modern science to probe the nature and evolution of a bewildering range of celestial objects. Man has even set out to call personally on his nearest neighbours in space. Professor Zdenek Kopal has lived and practised astronomy throughout this efflorescence of his subject. Born in Czechoslovakia just before the outbreak of the Great War, and educated in the classical European tradition, he knows well the days when scholars commanded such respect that astronomical congresses would be visited by Heads of State. Yet within his own lifetime, he has himself been recruited to play an important role in scientific preparations for a manned Moon landing. He has known and worked with some of the most highly respected practitioners of Modern Astromomy: Russell, Shapley, Urey in the United States, Eddington in Britain. His fine eye for detail, coupled with his strong sense of history, enable him to unfold through his personal recollections the development of his subject across the social changes of two world wars. Inspired by his grandfather, who would think nothing of walking sixty miles to theatrical performance, the young Kopal acquired a Wanderlust that has taken him in his career more than a dozen times rond the world. He has visited the most ancient observatories, observed solar eclipses in Japan and Java, helped to establish new institutions in Iraq and India, and commuted for many years between the Old and New Worlds. He has toiled in every corner of his chosen vinyard: as observer, outstanding theoretician, populariser, editor and teacher. During his thirty years as Professor of Astronomy at Manchester, he helped to educate over a hundered PhD students, many from the developing world, who have taken the torch of astronomy back to their home lands. In retirement, he continues to direct his efforts towards a better understanding of the Universe, and shows no sign of abandoning his life-long affair with the heavens. Professor Kopal has entitled his book Of Stars and Men, for he has delighted in the company of both throughout his life. The reader is invited to share with him the story of his birth, his education, his work and his travels; and to join with him in contemplating the history and possible future of his subject, and of civilisation itself.

Proceedings of the 97th Colloquium of the International Astronomical Union, held in Brussels, Belgium, June 8-13, 1987

The aim of the present book has been to provide an outline - the first of its kin- of the history of the human efforts to map the topography of the surface of our satellite, from the days of pre-telescopic astronomy up to the present. These efforts commenced modestly at the time when the unaided eye was still the only tool at the disposal of men interested in the face of our satellite; and were con tinued since for more than three centuries by a small band of devoted friends of the Moon in several countries. Many of these were amateur astronomers, and almost all were amateur cartographers; though some highly skilled in their art. The reader interested in the history oflunar mapping between 1600 and 1960 will find its outline in the first chapter of this book; and can follow the way in which the leadership in the mapping of the Moon, the cradle of which stood in Italy, passed successively to France, Germany, and eventually to the United States. All efforts described in this chapter were wholly superseded by subsequent devel opments since 1960, largely motivated by logistic needs of a grand effort which cul minated with repeated manned landings on the Moon between 1969-1972- a feat which will remain for ever one of the glories of our century."

After several decades spent in astronomical semi-obscurity, the Moon has of late suddenly emerged as an object of considerable interest to students of astronomy as well as of other branches of natural science and technology; and the reasons for this are indeed of historical significance. For the Moon has now been destined to be the first celestial body outside the confines of our own planet to be reconnoitered at a close range by means of spacecraft built and sent out by human hand for this purpose. At the time of writing, not less than ten such spacecraft of American as well as Rus sian origin landed already on different parts of the lunar surface; and some of these provided remarkable records of its detail structure to a spatial resolution increased thousandfold over that attained so far from our ground-based facilities. A renewed interest in our satellite, stemming from this source, on the part of the students of many branches of science and technology has also underlined the need for presenting the gist of our present knowledge in this field in the form that could serve as an introduction to the study of the Moon not only for astronomers, but also for serious students from other branches of science or technology.

Our conference - opening today - has two aims in view: first, to commemorate some milestones in the development of the studies of close binary systems whose anniversaries fall in these years, as well as to take stock of our present knowledge accumulated through out preceding decades, in order to consider where do we go from here. This summer, 310 years will have elapsed since the first ec lipsing binary - Algol - was discovered in Bologna by Geminiano Montanari (1633-1687) to be a variable star; and 198 years have gone by since John Goodricke of York (1764-1786) established the fact that Algol's light changes were periodic. Moreover, it is al most exactly (to a month) now 100 years since Edward Charles Pickering (1846-1919) of Harvard Observatory in the United States took the first steps towards the development of systematic methods of analysis of the light changes of Algol and related systems - a topic which will constitute the major part of the programme of our present conference. The three dates recalled above illustrate that the discoverers of such celestial objects and observers of their light changes have been systematically ahead of the theoreticians endea vouring to understand the significance of the observed data by de cades and centuries in the past - a fact which, incidentally, con tinues to hold good (albeit with a diminishing lead-time) up to the present.

The Bosscha Observatory in Lembang, Java, Indonesia, celebrated in 1983 its 60th anniversary. Since its foundation, the physical properties of binary systems have formed a major research topic of this observatory. Until 1970, the study of visual binaries and the determination of orbits received most emphasis. Since then, also the evolution of close binary systems, such as X-ray binaries, Wolf-Rayet binaries and binary pulsars, has been researched with priority in Lembang. It seemed thus appropriate that a Colloquium devoted to the study of binary systems be held in Lembang at the time of the Observatory's anniversary. In the Colloquium, the role of wide double (and multiple) systems received special emphasis - not only because of the long tradition of visual binary research at Lembang; but also because their role in documenting stellar evolution has been largely overlooked in recent decades, and needs to be brought into focus with the information forthcoming from close binaries. The Colloquium covered the physical properties of visual as well as close binary systems, and their generic relations, in the broadest possible sense. It was sponsored by the International Astronomical Union as IAU Colloquium No. 80 ('Double Stars, Physical Properties and Generic Relations'). After the official opening ceremony, the meeting started with a discussion on the future of astronomy in Asia. The scientific sessions began with the 'V. Bappu Memorial Lecture on the Evolution of Binary Systems', presented by Z. Kopal.

After many decades spent in astronomical semi-obscurity, the Moon has of late suddenly emerged to claim renewed interest on the part of the students of astronomy, as well as of other branches of physical science and technology; and the reasons which brought this about are indeed of historical significance. From time immemorial, astronomy has been debarred from the status of a gen uine experimental science by the utter remoteness of the objects of its study. With the exception of meteors - those small freaks of cosmic matter intercepted by the Earth on its perpetual journey through space - the properties of all celestial bodies outside the gravitational confines of our planet could be studied only at a distance: namely, from the effect of attraction exerted by their masses; or from the ciphered message of their light brought to us by nimble-footed photons across the intervening gaps of space. A dramatic emergence of long-range rockets in the last decade bids fair to bring about a profound change in this situation. On September 13, 1959 - a memorable date in the history of human endeavour - a man-made missile of Russian origin crash landed on the surface of the Moon in the region of its Mare Imbrium, and thus ended the age-long separation of the Earth and its only natural satellite which lasted not less than 4t billion years."

If Zdenek Kopal Department of Astronomy University of Manchester Your Magnificences, my Lord Mayor, ladies and gentlemen! It is a great pleasure for me to respond, on behalf of your foreign guests, to your gracious words of welcome; and to thank you for the wonderful reception which you nave extended to us. The city of Bamberg and its Remeis Sternwarte nas indeed been renowned allover the world for a great many years - as the place where your Observatory's first director, Professor Ernst Hartwig (1851-1923) - in addition to his other titles to fame - collaborated (with Gustav Muller of Potsdam) on the construc- tion of the monumental Geschichte und Literatur des Lirhtwechsels der Veranderlichen Sterne, which since 1918 has (together with its sub- sequent continuation) been a veritable vade-mecum of a1l students of variable stars; where the second director, Professor Ernst Zinner (1886-19]~ prepared his valuable Katalog der Verdachtigen Veranderlichen Sterne (192@ which safeguarded many an astronomer (including the present speaker in the days of his innocence) from premature discovery claims; and whose third director, Professor Wolfgang Strohmeier, initiated in 1959 the tradition of the international colloquia of which ours is the latest successor. It is indeed a great pleasure to welcome Professor Strohmeier - now Emeritus - among us; and to congratulate him on the grace with which he is carrying his years.

The aim of the present book will be to provide a comprehensive account of our present knowledge of the theory of dynamical phenomena exhibited by elose binary systems; and on the basis of such phenomena as have been attested by available observations to outline probable evolutionary trends of such systems in the course of time. The evolution of the stars - motivated by nuelear as weIl as gravitation al energy sources - constitutes nowadays a well-established branch of stellar astronomy. No theo ries of such an evolution are as yet sufficently specific - let alone infallible - not to require continual tests by a confrontation of their consequences with the observed prop erties of actual stars at different stages of their evolution. The discriminating power of such tests depends, of course, on the range of information offered by the test objects. Single stars which move alone in space are now known to represent only a minority of objects constituting our Galaxy (cf. Chapter 1-2); and are, moreover, not very revealing of their basic physical characteristics - such as their masses or absolute dimensions. If there were no binary systems in the sky, the only star whose vital statistics would be fully known to us would be our Sun.

A favourable reception of the first edition of this book - due no doubt to the nature of its subject - which went out of print in 2 years, gave its author a welcome oppor tunity to update at present its contents. This was all the more necessary, as seldom in the annals of science has our knowledge of the physics and astronomy of the Moon made greater progress than during this time. The real heroes of this advance have, of course, been the spacecraft - 33 of which have now been sent out since 1959 to reconnoiter our satellite at a close range. The hard-landers among them just about delivered their message by the time when the first edition of this book went to the press; but it was the soft-landers and orbiters, which followed in their wake between 1966-67, that became really the principal contributors to lunar research. By now that it may be both timely and their programmes have likewise been completed; so opportune to take stock of the present state of our subject now - on the eve of the next stage of lunar exploration by manned landings on the surface of our satellit- which can be expected to take place in the very near future. * The aim of the second edition of this book will be to provide the requisite infor mation, brought up to date in an organized manner."

The words of this preface were written when the book was ready to go to the press; and are limited to only a few points which are best made in this place. As is intimated by the sub-title, the whole volume was written with appli cations in mind to double-star astronomy. The latter is, however, not the only branch of our science which could benefit from its contents. The same is true of certain aspects of the dynamics of stellar systems or galaxies (the stellar popula tions of which are also characterized by the fact that the mean-free-path of their constituent stars are long in comparison with the dimensions of the respective systems); the central condensations of which are high enough to approximate the gravitational action of a "mass-point." This fact did not, to be sure, escape the attention of previous investigators (in the case of globular clusters, in particular, the Roche model was introduced in their studies under the guise of polytropic models characterized by the index n = 5); though no particular attention will be paid to these in this book. But possible applications of the Roche model are not limited to problems arising in stellar astrophysics. With Coulomb forces replacing gravitation, the equilibrium model finds a close analogy in the field of electrostatics-as was pointed out already at the beginning of this century by (then young) J. H. Jeans (cf."

ASTRONOMICAL ECLIPSE PHENOMENA In looking over the long history of human science from time immemorial to our own times, it is impossible to overestimate the role played in it by the phenomena of eclipses of the celestial bodies-both within our solar system as well as in the stellar universe at large. Not later than in the 4th century B. C. , the observed features of the shadow cast on the Moon by the Earth during eclipses led Aristotle (384-322 B. C. ) to formulate the first scientific proof worthy of that name of the spherical shape of the Earth; and only somewhat later, the eclipses of the Sun provided Aristarchos (in the early part of the 3rd century B. C. ) or Hipparchos (2nd half ofthe same century) with the geometric means to ascertain the distance which separates the Earth from the Sun. In the 17th century A. D. (in 1676, to be exact) the timings of the eclipses of the satellites of Jupiter by their central planet enabled Olaf Romer to discover that the velocity with which light propagates through space is finite.

During the past years, a number of international astronomical conferences were held at the Remeis-Observatory in Bamberg, four of them sponsored by the International Astronomical Union. The first meeting was organized in 1959 and dealt with Variable Stars, the last one was held in 1981 and focussed on 'Binary and Multiple Stars as Tracers of Stellar Evolution'. The present conference was organized to commemorate the 200th anniversary of the birth of Friedrich Wilhelm Bessel, who was born in Minden on July 22, 1784, and died in Konigsberg on March 17, 1846. When the plan for an international conference on astrometric binaries was presented to several colleagues, we received enthusiastic support and decided to pursue the idea. A Scientific Organizing Committee was soon established, consisting of: Z. Kopal Manchester, u.K. S. M. Gong Nanjing, China (Chairman) M. Grewing Tiibingen, F.R.G. V. Abalakin Pulkovo, U.S.S.R. P. v. d. Kamp Amsterdam, Netherlands J. Dommanget Uccle, Belgium M. Kitamura Tokyo, Japan M. G. Fracastoro Torino, Italy J. Rahe Bamberg, F.R.G. W. Fricke Heidelberg, F.R.G. Ya. Yatskiv Kiev, U.S.S.R. E. H. Geyer Bonn, F.R.G. The meeting took place in Bamberg at the Remeis-Observatory, Astronomical Institute of the University Erlangen-Nurnberg, from June l3 to 15, 1984. The following institutions generously supported the meeting: Deutsche Forschungs- gemeinschaft, Bonn; Stadt Bamberg; Universitat Bamberg; Universitat Erlangen- Nurnberg; University of Manchester.

Eclipsing Variables - What They can Tell Us and What We can do with Them The aim of the present book will be to provide an introduction to the inter pretation of the observed light changes of eclipsing binary stars and their analysis for the elements of the respective systems. Whenever we study the properties of any celestial body - be it a planet or a star - all information we wish to gain can reach us through two different channels: their gravitational attraction, and their light. Gravitational interaction between our Earth and its celestial neighbours is, however, measurable only at distances of the order of the dimensions of our solar system; and the only means of communication with the realm of the stars are their nimble-footed photons reaching us - with appropriate time-lag - across the intervening gaps of space. As long as a star is single and emits constant light, it does not constitute a very revealing source of information. A spectrometry of its light can disclose, to be sure, the temperature (colour, or ionization) of the star's semi-transparent outer layers, their chemical composition, and prevalent pressure (through Stark effect) or magnetic field (Zeeman effect), it can disclose even some information about its absolute luminosity or rate of spin. It cannot, however, tell us anything about what we should like to know most - namely, the mass or size (i.e., density) of the respective configuration; its absolute dimensions, or its internal structure."

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. Astronomy is one of the oldest branches of science conceived by the inquisitive human mind; though until quite recently it had been debarred from the status of a genuine experimental science by the remoteness of the objects of its study. With the sole exception of meteoritic matter which occasionally finds its way into our labora tories, all celestial bodies could be investigated only at a distance: namely, from the effects of attraction exerted by their mass, or from the ciphered messages of their light carried by nimble-footed photons across the intervening gaps of space. A dramatic emergence oflong-range spacecraft -capable of carrying men with their instruments not only outside the confines of our atmosphere, but to the actual surface of our nearest celestial neighbour - has since 1957 thoroughly changed this time honoured picture. In particular (as we shall detail in Chapter 1 of this book) space astronomy ofthe Moon is barely 15 years old. But relative infant as it is by age, it has already provided us with such a tremendous amount of new and previously inacces sible scientific data as to virtually revolutionalize our subject."