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Nearly 19 years of rapid scientific progress have elapsed since Mihalas & Binney went to press. In these years, there have been fundamental changes in the way that we approach the study of galaxies. Spectacular advances in telescope and detector technology, and in the scale of space observatories, have enormously enriched the quality of the data that are available, particularly for external galaxies. Although some details of galactic structure are still best studied using our uniquely close-up view of the Milky Way, the over-all picture can be seen most clearly from the perspective afforded by observations of other galaxies. The emphasis in studies of galactic structure has therefore shifted toward exploiting the wealth of extragalactic observations that is now available, and the layout of this book has been altered from that of Mihalas & Binney to reflect this change.
It remains important to understand the historical development of the subject, and essential to have a good grasp of fundamental astronomical concepts, so the first three chapters still cover the history of galactic astronomy, astronomical measurements and the phenomenology of stars. We then turn directly to the morphology of external galaxies -- Chapter 4 gives a broad perspective on the different types of galaxies that populate the Universe. Chapter 5 reviews the theory of stellar structure and nucleosynthesis insofar as it bears on the ages and evolutionary histories of galaxies. The simplest applications of this theory are to star clusters, which form the subject of Chapter 6. Chapter 7 covers the sometimes tortuous lines of reasoning that are used to deduce distances in the Universe, and hence estimate such basic parameters as the sizes of galaxies and the distances between them. Chapters 8 and 9 are concerned with the structure and dynamics of the interstellar medium, in external galaxies and in the Milky Way, respectively. The interstellar medium has provided a wealth of information on the dynamics and the chemical evolution of galaxies. It also determines the rate at which stars form, which, in turn, profoundly influences the optical appearance of galaxies. Our study of the Milky Way gets under way in earnest with Chapter 9 and continues into Chapter 10, which complements the interstellar studies of Chapter 9 with a coherent picture of the distribution of the Galaxy's stars. The study of stars near the Sun is particularly rewarding because we can analyze their motions and chemical compositions in great detail. A wealth of information about the dynamics and history of the Galaxy can be gleaned from such analyses. Chapter 11 completes the book by covering our knowledge of the motions of stars within external galaxies.
In a subject area as broad as galactic astronomy, we have inevitably had to compromise on the material that we have included in the book. Moreover, it is impossible to be familiar with every relevant publication, and we have surely based some discussions on older or less satisfactory papers than we might have done. We apologize to the colleagues we have unfairly neglected, and trust that they will forgive us for not chasing the unachievable goal of a truly comprehensive work.
Throughout, we have tried to present basic observational data, and let readers decide for themselves how firmly they believe the conclusions that have been drawn from them. Since one cannot avoid drawing on a good deal of theory for the interpretation of observational data, we review any theoretical details that are likely to be unfamiliar to a student who has a solid background in undergraduate physics. We have, however, sought to ensure that theory and observation are kept clearly separated, to enable students to distinguish raw facts from their model-dependent interpretation.
In a few places, we have borrowed text directly from BT; the intention is to drop borrowed material from any revised edition of that work. At many points, we refer the reader to BT for the discussion of more theoretical topics such as the derivation of a dynamical result, or the explanation for a dynamical process. As far as possible, the notation in this book is the same as that in BT.
For more than thirty years now, most undergraduate physics courses have employed SI units. Feeling that it is time that the astronomical literature reflected this development, we decided -- with some trepidation -- to use SI units. Our hope is that the present generation of graduate students will finally start to publish in SI units, and, by doing so, make life less perplexing for generations to come.
JJB wishes to thank the Director and staff of the Mount Stromlo and Siding Spring Observatories for their warm hospitality during an important phase in the writing of this book. We thank D. Hartmann, H. Morrison and M. Strauss for carefully commenting on some draft chapters. Finally, we thank the numerous colleagues who have shared with us their thoughts, ideas, data, and figures. Many of our 330 figure captions mention a specific case of such debt. Although we shoulder full responsibility for any shortcomings and inaccuracies in the book, any credit must be widely shared across the entire astronomical community. We hope that this text represents a fitting tribute to the progress that the community has made in the study of galaxies, and that it will help in taking stock of the many important tasks that still lie ahead.
1998 May 1
James Binney
Michael Merrifield