Reviewing a science text for high-school honors courses

Project STAR: The Universe in Your Hands
1993. 384 pages. ISBN: 0-8403-7715-0.

This textbook, copyrighted by the President and Fellows of
Harvard College, is printed and sold by the Kendall/Hunt
Publishing Company, 4050 Westmark Drive, Dubuque, Iowa 52002.

The book is a product of Project STAR, a program that was
sponsored by the Harvard-Smithsonian Center for Astrophysics and
supported by the National Science Foundation. The acronym STAR
stands for Science Teaching through its Astronomical Roots.

For Serious Teachers and Students,
This Book Is Just the Thing

Lawrence S. Lerner

Our purpose is simple: To help you learn about science. Our philosophy is more complicated: We believe you learn science better by making measurements and observations than by memorizing "facts." Understanding science also requires understanding concepts, which are mostly much harder to learn than facts. But a single concept, or theory, can usually allow you to understand a large number of facts. . . . Everybody has ideas about how the world works; we believe your teacher should ask you about your ideas first and then help you to test their accuracy by showing you how to make the relevant measurements and observations.

As that excerpt indicates, Project STAR is not, and does not claim to be, an encyclopedic survey of astronomy. It is a book built around investigation and observation, and it puts much emphasis on measurements. Most of the measurements are made with simple devices, and many of the devices are constructed by the student.

The book has fifteen chapters, each dominated by one or more activities. A typical chapter begins with a set of questions, then presents three or four activities and a concluding discussion. The discussion gives the student a theoretical basis for understanding what the activities have demonstrated, and it ends with "Homework" and "Self-Test" problems. (Curiously, the discussion in every chapter uses future-tense verbs in referring to things that the student already has done; this suggests that the discussion was originally intended to be placed before, rather than after, the activities. In chapter 3, for instance, the discussion starts on page 57, and it tells the student that he "will" construct a celestial sphere and "will" use the sphere to explore the reasons why Earth has seasons. But the student has already done those things, in activities that were given on pages 44 through 56.)

The chapter-opening questions serve an interesting purpose. Before the student does any reading, he is asked to write down his answers to queries about topics that the chapter will consider, or he is asked to gather answers by surveying his friends, parents or teachers. Later, as he studies the chapter, he probably will learn that his initial answers, or those that he gathered from his acquaintances, were incorrect. The questions have been calculated to expose common misconceptions, as some examples will show: Why is the weather warmer in summer than in winter? If you look at the North Star through a department-store telescope, is the star's image bigger or smaller than (or the same size as) the image that you see with your naked eye? What is a galaxy? -- and how many galaxies are there in the universe? A couple who have four sons are expecting another child: Will the new baby more probably be a boy than a girl? Will it more probably be a girl than a boy? Or are both possibilities equally likely?

The 39 activities in Project STAR require care and diligence, but they rarely require any complicated equipment. To measure angles, the student compares them with the angle subtended by his finger, his hand or his fist (held at arm's length), and this usually eliminates the need for trigonometric formalisms. To make a Rumford photometer, which the writers call a "wax photometer," he uses paraffin blocks and aluminum foil.

Unfortunately, some of the activities will not work well. One of the earliest, Activity 1.2, asks the student to trace the Sun's path through the sky in a simple and clever way. Given a plastic hemisphere, the student centers it on a point marked on a horizontal piece of white cardboard; then he moves the point of a wax pencil until the shadow of the tip of the pencil falls onto the center point, and he makes a mark on the hemisphere. A series of such marks, made over a reasonable period of time, will nicely describe the path of the Sun -- but alas, the Project STAR writers allow the student to make only three marks, over a period of 30 minutes. While this enables the student to complete the activity during one class period, it means that the marks on the hemisphere will be very close together. Any attempt to extrapolate the diurnal path of the sun from such closely grouped points will probably fail. (The writers are aware of this, and they later ask the student to perform the same exercise during a weekend, making measurements throughout an entire day. This can yield excellent results, but how many students will actually do it?)

Some other activities present a difficulty that is unavoidable: They require the student to observe stars or planets at night, or to make measurements at sunrise or sunset. These tasks have to be performed outside of class, of course, and the student will not be able to solicit help from his teacher if he runs into trouble.

Nevertheless, a persistent student will learn a goodly amount of astronomy and a great deal about doing science. The Project STAR activities lead the student through observations of the daytime sky, then through observations of the nighttime sky, and thence to model-building and simple astrometry. Many students (and many teachers as well) will probably be astonished to see how much they can infer from a set of crude but cleverly conceived measurements.

Activity 5.1 is a lovely experiment in which the student learns the inverse-square law for brightness by utilizing an unfrosted light bulb and a graph-paper grid. Light from the bulb passes through a square hole in a piece of cardboard, then falls onto the grid (whose squares have the same size as the hole in the card). As the student moves the grid farther and farther from the piece of cardboard, he records the number of grid squares that receive illumination, and he soon finds that this number varies with the square of the distance between the bulb and the grid. (There is one tricky bit, though. The writers don't explain that the bulb must have a linear filament, which can be turned end-on to approximate a point source of light. This is not the kind of filament found in the bulbs sold by supermarkets; if the student tries to use a supermarket bulb in performing Activity 5.1, the penumbra cast on the grid may cause substantial errors.)

From such modest beginnings, the student progresses to more sophisticated undertakings. Given a series of pictures that show the apparent size of Venus as it passes through its phases, the student is led to understand why the Copernican picture of the solar system is correct. Given a diagram that shows how the apparent diameter of the Sun varies during the year, the student estimates the eccentricity of Earth's orbit, and he learns that the seasons do not depend on the Sun-to-Earth distance. Later, the student makes a small refracting telescope, measures its magnification, observes various objects through the telescope, and determines how far away they are; and the writers explain that one can determine an object's absolute size if the object's distance is known, or vice versa. Still later, the student learns how to make apparent-brightness and intrinsic-luminosity estimates for stars.

With an inexpensive diffraction grating, the student builds a cardboard spectrometer and a crude "colorometer," and he makes some simple spectral measurements. The writers introduce the Hertzsprung-Russell diagram (although they do not call it by that name), and they lead the student to make some inferences about the nature of stars. Inevitably, the amount of measurement that the student can perform diminishes as the book's astronomical scope expands, but the book's emphasis on observation, modeling and investigation is maintained throughout. The last, delightful chapter, which introduces the student to probability theory, includes an activity that demonstrates the silliness of astrology.

Project STAR presents some exemplary historical material, such as the explanation of why Columbus was obliged to convince his backers that the smallest available estimates of Earth's dimensions were the correct ones -- which they were not! There are also some failures, however. The account of the Ptolemaic model of the solar system is muddled, and the writers have erred badly in presenting and interpreting an engraving of Tycho Brahe and his mural quadrant (page 40). They have cropped the part of the engraving that shows how Tycho actually used the quadrant in making observations, and their caption suggests that they don't understand what the name "mural quadrant" means. (It means that the quadrant was mounted on a curved wall -- not that the quadrant stood near a mural painting which depicted Tycho's observatory, instruments and assistants.) And it is misleading, at least, to say that when Annie Jump Cannon went to college (in 1884), she was "one of the first women from her home state of Delaware to do so." The writers' implication -- that it was novel and remarkable for a woman to go to college in 1884 -- is false. Oberlin College, founded in 1833, had admitted women from the outset, and by 1884 the United States had numerous women's colleges and coeducational colleges.

There are a few scientific mistakes as well. For example, the description of the photoelectric effect is wrong; light shining on a metal does not increase the metal's conductivity, as the description implies, but causes emission of electrons from the metal's surface. The two blackbody-emission spectra shown on page 259 are so different in shape that they cannot both be correct. And it surely is not true that you can see "even in the darkest room."

Finally, there are some pedagogic mistakes or oversights. The writers introduce the concept of fixed stars by saying that "The stars . . . always seem to have the same positions with respect to each other," but they fail to give a clear, unambiguous explanation of the physics embodied in that phrase "with respect to each other." Some of the drawings (such as those on pages 32 and 34) seem too crude to convey the information they are intended to convey. The statement that "The size of the unit area depends on the units in which the area . . . is measured" is confusing nonsense (page 111). The statement that light is "mysterious" is silly (page 113). The account of how Cepheid variables and RR Lyrae stars are used in finding astronomical distances is not as clear as it should be. In particular, the writers don't explain the crucial point that the absolute calibration of Cepheids requires observations of one or more Cepheids whose parallax is known. (This is a surprising lapse in a book that devotes so much space to the relations among distance, absolute size and angular size.) These slips, and some others like them, should be corrected when Project STAR goes into its next edition.

The writing, overall, is rather dull but acceptable, given that much of the book consists of detailed descriptions of activities. The problems presented to the student are generally interesting, and challenging, and some of them have practical implications. (An example is the problem on page 72, which leads the student to see how eaves can keep summer sunlight out of a house but permit winter sunlight to enter.) The copy-editing seems good; I detected only five or six typographical errors in the whole book.

Project STAR is accompanied by a fine Teacher's Guide which provides thoughtful, clear answers to problems, and which deals thoroughly with the pitfalls that may be encountered in performing the activities. It even warns the teacher about instances in which students may try to fudge their results, and it proffers advice about forestalling such fudging. The Project STAR writers have obviously worked carefully through their own material!

Who will benefit from using this good book? Not the teacher who wants to "cover" all of astronomy, and not the student who is unwilling to expend time and effort in studying and in doing laboratory work. But for the teacher who wants to teach real science, and for the student who wants to learn to think like a scientist, Project STAR is just the thing.

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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