from The Textbook Letter, March-April 1997

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

I like to make a distinction between teaching science and teaching about science. Introductory courses in astronomy often take the latter road, thus satisfying the student's need for some science credits without putting him under much mental stress. As a consequence, most introductory astronomy textbooks are purely descriptive, usually encyclopedic, tours through the universe, with plenty of rubbernecking but little inquiry.

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.

An Ingenious Path

The writers of astronomy texts face a crucial choice as soon as they begin to organize their material: Should the presentation be "inside-out" or "outside-in"? Traditionally, astronomy has been taught from the inside out. One begins with the Moon, the Sun, the planets and the solar system, and then one gradually works outward to consider the Milky Way, galaxies in general, and finally the universe as a whole (with the cosmological questions that it poses). This approach recapitulates the historical development of astronomy, and it allows the student to start with the celestial objects that are most familiar to him. Its great disadvantage is that the problems which occupy most of today's astronomers are left until last. They may get less attention than they deserve, or they may even be skipped entirely, for lack of time.

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.

A Few Mistakes

The historical discussion is far more accurate than most that I have seen, but it does contain some lapses. On page 64, for example, Seeds points out that we usually refer to Tycho Brahe by his first name. "Were he alive today," Seeds remarks, "he would no doubt object to such familiarity from his obvious inferiors -- he was well known for his vanity and lordly manners." Perhaps. But in Renaissance times, eminent persons were often designated by their first names alone, and this was not regarded as a display of familiarity or condescension. Examples include Galileo (Galilei), Michelangelo (Buonarotti), Dante (Alighieri) and, for that matter, all the kings and queens in Europe.

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.


To use this fine textbook in a high-school course, the teacher must deal intelligently with the book's main foible: Like the writers of so many other "survey" texts, Seeds has tried to cover too much and has sometimes given too much detail. The teacher therefore must cut Exploring the Universe by letting students skip some of its more arcane or overdone sections. This cutting should be a rather easy task. Here are some suggestions:

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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