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Sol Searching

Steve Kawaler

Sunquakes: Probing the Interior of the Sun.
J. B. Zirker.
xiv + 265 pp. The Johns Hopkins University Press, 2003. $29.95.

In a sense, solar astronomy suffers from an image problem. Our Sun remains, for the most part, as enigmatic as it was thousands of years ago. Yet the general public, and even most astronomers, seldom think about its mysteries. Solar physics is rarely mentioned in the newspaper except on the occasion of eclipses or solar flares that generate auroral displays. But now readers can get a sense of how exciting the field can be from the remarkable book Sunquakes: Probing the Interior of the Sun, by J. B. Zirker, astronomer emeritus at the National Solar Observatory in Sunspot, Arizona.

The book's focus is the development of the relatively new scientific discipline of helioseismology—the study of subtle vibrations that we see on the surface of the Sun. Detection of these oscillations in the early 1960s was a technical tour de force. It required the measurement of extremely subtle Doppler shifts in spectral lines, which signal wavelike motions of the solar surface. Understanding the nature of these vibrations as acoustic oscillations (organized sound waves) allowed scientists to use them to probe, in detail, the structure and dynamics of the inside of the Sun in much the same way that terrestrial seismology has revealed the internal structure of the Earth. Sunquakes provides an excellent, comprehensive overview of the history of the field, from the early discoveries of the 1960s through the establishment of current Earth-based and space-based helioseismology programs. Lucid discussions of the scientific principles and challenges of the quest to understand solar oscillations are interspersed with anecdotes revealing the personalities involved.

I wish that such a book on solar astronomy had existed when I was a graduate student and had the notion that solar astronomy was less than thrilling. Luckily, I learned otherwise during a postdoc at Yale from 1986 to 1989, where I helped model the rotating solar interior, discovering firsthand the intellectual challenges of solar physics. There I had the opportunity to meet many of the scientists profiled in Sunquakes. Although I now study the seismology of other stars, solar astronomy remains a strong interest of mine.

This book demonstrates how much a few dedicated individuals can accomplish in a relatively short time. Helioseismology was developed and continues to thrive through the cooperative efforts of theorists, instrument builders and other highly motivated people. Zirker does discuss some of the more contentious debates within the field, in the process acknowledging the fierce competitiveness of the researchers. More important, he makes the point that broad cooperative collaboration can accelerate progress in a field and be fun at the same time.

Helioseismology is a key tool for studying complex subjects such as stellar convection and the origin of the solar magnetic field. Discoveries by helioseismologists about the internal structure of the Sun also eliminated the astronomical uncertainties in the "solar neutrino problem" (why we detect far fewer electron-flavored neutrinos than standard theory predicts are emitted from the nuclear engine of the Sun) and helped focus efforts to find the explanation in terms of particle physics.

Sunquakes is a remarkable book that conveys a true sense of the excitement involved in the development of a new scientific discipline. The main body of the text discusses the science with accuracy and at a level appropriate for a general readership. Zirker reserves more detailed discussions for chapter notes, which appear at the end of the book and display the same ease of style and level of precision as the main text. As is inevitable in such a book, there are a few minor inaccuracies, but these should not detract from the reader's enjoyment.

There may never be a "best time" to compile a story about an active research area. By definition, such areas are fluid and changing rapidly, so what seems to be the dominant paradigm at the moment can be dramatically altered in short order. Given this, Zirker has certainly captured the essence of helioseismology for the present day. This book is a well-timed and capable recounting of the birth and maturation of the field.—Steven Kawaler, Physics, Iowa State University

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