Reviewing a science book for high-school honors courses

Horizons: Exploring the Universe
1995. 484 pages + appendices. ISBN: 0-534-24889-6.
Wadsworth Publishing Company, 10 Davis Drive, Belmont, California 94002.
(Wadsworth is a part of International Thomson Publishing Inc.)

A Commendable Textbook
That Really Teaches Some Science

Lawrence S. Lerner

Michael A. Seeds's Horizons: Exploring the Universe, written as an introductory college textbook, manages to do something more. It really does teach some science. While Seeds's treatment of astronomy is almost entirely descriptive and nonquantitative, he provides a fair amount of analytical discourse -- and the chapter-end problems, though few in number, often stimulate genuine scientific thinking. Thus Exploring the Universe affords the beginning student an entree into science that is both serious and friendly.

With some caveats, which I shall present shortly, I regard this book as entirely suitable for use in a high-school honors course.

The outside-in approach is more modern and more consonant with what today's astronomers actually do, but it presents pedagogic difficulties. It requires the student to deal immediately with unfamiliar things, and it necessitates the immediate introduction of some unfamiliar aspects of modern physics.

In Exploring the Universe, Seeds chooses an ingenious middle path. He begins with a description of the sky as seen by the naked eye, and he establishes relatively familiar landmarks for later study. In doing this, he shows how astronomers of earlier times used observation, modeling, quantitative analysis and theory-building to construct the foundation on which modern astronomy is based. Then he introduces, not necessarily in historical order, the modern astronomer's tools: optical telescopes, spectrometers, photometers, and telescopes for observing the nonvisible parts of the electromagnetic spectrum (from radio waves to X rays). Next, he bypasses any detailed discussion of the solar system so that he can deal with the stars, the galaxies and the universe as a whole. Then, in his closing chapters, he presents a detailed examination of our solar system and of the conditions that favor the evolution of life in such a system.

The discussion of stars, in particular, is clearly based on inquiry. Seeds uses the Hertzsprung-Russell diagram extensively and effectively, first to impose order on the bewildering array of stars and then as a powerful analytical tool for tracing stellar life cycles. The student is led carefully through the evolution of both common and unusual stars, and he should be able to see how various stellar histories fit into a large and consistent picture.

Seeds is diligent in conveying the varying degrees of confidence that astronomers have in their interpretations of various phenomena. It is unlikely that a student who uses this book will acquire the misconception that astronomy is a body of absolute truths, brought down from Mount Sinai. Rather, the student will see that astronomers are engaged in a dynamic endeavor, always grappling with uncertainty as they improve their knowledge and test their understanding of how the universe works.

Exploring the Universe is extensively and beautifully illustrated, and the illustrations are almost always relevant to the science that is being taught. Seeds does not use boxes, sidebars or feature articles as parking places for gimcracks. He uses them, judiciously, to present mathematical and technical arguments that are at a somewhat higher level than the material in the book's main text. Particularly impressive is the "Perspective" article titled "Climate and Ice Age" (pages 52 to 54). Here Seeds discusses the Milankovitch hypothesis of long-term climatic change, citing both positive and negative evidence. The fact that "simple" ideas often have complex qualifications and ramifications is made very clear.

Figure 4-13 (page 66) is a "colorized" version of a famous etching of Tycho's laboratory, featuring his large, precise angle-measuring device known as the mural quadrant. It is called by that name because it was mounted on a wall; the Latin word for wall is murus. But Seeds misinterprets the name and says that the etching shows "a mural painted on the wall within the arc of the quadrant." He is not alone in his confusion, for other writers have made the same mistake. See, for example, my review of Project STAR in The Textbook Letter, July-August 1996.

Two more historical mistakes appear on the next two pages: Kepler had to defend his aunt, not his mother, against charges of witchcraft; and Kepler favored magnetism, not gravity, as the force that holds the solar system together.

There are some editorial errors, but only a few of them are serious. Figure 5-26 is missing. The text on page 103 says that figure 5-30 shows "the Advanced X-ray Astrophysics Facility," but figure 5-30 actually shows the Hubble Space Telescope and one of the photographs that the telescope has made. On page 190, Seeds asks the reader to "Recall from Einstein's equation E = mc² that energy and mass are related." But that equation has not been introduced -- and even though most students have heard of it, few students have any idea of what it means. On page 325, the explanation of the curvature of space contains two mathematical mistakes that the editors should have caught: A saddle has both positive and negative curvature, not just negative curvature; and the area that a circle of radius r encloses on a positively curved surface is greater, not smaller, than the area that a circle of radius r encloses on a plane. Finally, there is a glaring mistake in the book's index: Einstein's first name is given as "Alfred" instead of Albert.

• In chapter 6, the discussion of the spectral classification of stars seems too heavy. I personally find it interesting, but I think that it will exhaust any student who doesn't already know the details of the Bohr-Sommerfeld theory of atomic structure. Something simpler would serve here.

• In chapter 7, the discussion of sunspots is too long -- especially because a typical student will not have enough background to appreciate the implicit subtleties. In an introductory course, the study of the Sun should focus on its role as a smallish or medium-sized star, the reactions that produce energy at its center, and the transmission of energy from the center to the Sun's surface.

• In chapter 12, the discussion of Cepheid variables is unnecessarily complicated and mystifying. Seeds should have used a simpler approach. Why didn't he discuss calibration in terms of the Cepheids seen in the Magellanic Clouds?

• The unit on the solar system, with its "Data File" sections about the Moon and the various planets, has more detail than beginners can use. Instead of asking students to read all of this unit, the teacher can extract the most important material and present it in some classroom lectures. The lectures, I suggest, should emphasize the evolution of the solar system as a whole, the evolution of the earthlike planets, and the evolution of life.

Other readers, I'm sure, will make other choices to achieve the same end. As Rudyard Kipling once wrote:

There are six and ninety ways of constructing tribal lays,
And every single one of them is right.

Exploring the Universe is right too, in six and ninety ways at least, and I recommend it warmly.

Lawrence S. Lerner is a professor in the Department of Physics and Astronomy at California State University, Long Beach. He served on the panel that wrote the current framework for science education in California's public schools, and he is a director of The Textbook League.

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