Reviewing a middle-school book in the Prentice Hall Science series

Editor's Introduction -- Prentice Hall's Exploring the Universe belongs to the Prentice Hall Science series, which comprises nineteen books that are sold for use in middle schools. The original versions of all nineteen were dated in 1993 (though they actually were issued in 1992). The Prentice Hall Science series includes some of the worst "science" textbooks that we ever have seen. We published reviews of some other books in the series in 1992, 1993 and 1994.

Star Dreck

Leonard Tramiel

Astronomy is a superb way to introduce young students to science. Even in urban areas that are plagued by smog and by light pollution, nearly everyone has seen things in the night sky and has wondered about them. A teacher can start with such common phenomena as the phases of the Moon or the cycle of the seasons, then use these to elucidate the fundamental operations of science: observation, generalization, prediction, experimentation and (most important) revision. All these can be introduced in both a personal and a historical context. Astronomy is rich in facts that students seem eager to learn, and a teacher can easily show students how astronomy is linked to topics and images that appear every day in newspapers, on television, and even in pop music -- from comets to black holes to the search for extraterrestrial intelligence.

Astronomy is a superb way to introduce young students to science -- but Exploring the Universe is a terrible way to teach astronomy. This book is full of mistakes, ranging from simple misspellings and factual errors to passages in which concepts have been mangled so badly that they are recognizable only by their names. Even when errors and misconceptions do not completely obscure the material that Prentice Hall's writers are trying to deal with, there is no effort to connect that material to the broader aspects of science.

Early in the first chapter, on page 12, Prentice Hall's writers say: "Most scientists believe that nothing can travel faster than the speed of light, . . . ." This is an early, accurate indication that Exploring the Universe will not be useful for teaching science's basic precepts. In a scientific context, what people "believe" is not an issue. The things that matter are observations and reason and predictions from scientific theories. By couching a topic in terms of belief, the writers not only have lost an opportunity to teach about science but also have reinforced a perception that is false.

In this review I will describe only some of the defects that I have seen in Exploring the Universe, because I don't have space to list them all. I will concentrate first on the book's factual and conceptual failings. Later in the review, I will cite passages in which the book teaches false "history," promotes pseudoscience, and affirms popular beliefs that have no foundation in truth.

• On page 15: "Astronomers believe [!] that almost all novas are members of binary-star systems." Why has this statement been watered down by the insertion of "almost"? Novas are binary stars -- and the recognition that novas are binaries has enabled us to explain many other astronomical phenomena. Prentice Hall's writers have obscured an important fact and have squandered an opportunity to show how an understanding of one aspect of nature can help us to understand other aspects.

• Page 17: A caption says that one of the objects shown in figure 1-7 is the Red Nebula. I haven't been able to identify the object, but I know that it is not the Red Nebula.

• Page 18: "In fact, astronomers now believe [!] that there may be more than 100 billion major galaxies, each with billions of stars of its own." On the same page, the caption for figure 1-8 says: "Each galaxy in this cluster of galaxies might hold several trillion or more stars."

• Page 20: "Earth's sun, along with many of the stars in the spiral arms, is among the younger stars in the Milky Way." This is meaningless. Some stars will endure for more than 100 billion years, some for only a few million. Our Sun is now about 5 billion years old and will last for 5 billion years more. Some stars in the Milky Way are older than the galaxy itself, while others originated only a few hundred thousand years ago. The Sun is not one of the oldest stars in our galaxy, but this does not mean that it is one of the youngest.

• Page 22: The caption for figure 1-13 says, "Parts of the constellation Sagittarius are seen in this X-ray photograph (bottom left)." No, the photo shows the remnant of a supernova in Cassiopeia.

• Page 23: In a diagram of a spectroscope, the order of the colors in the spectrum is backward.

• Page 24: In a passage about the red shift and the Doppler effect: "In fact, wavelengths from an approaching star often appear shorter than they really are." Often? No, they always appear shorter. What have the writers tried to gain by weakening their statement? I notice that when they deal with the opposite case -- the case of a star that is receding from Earth -- they don't equivocate by saying that the wavelengths from such a star "often" or "sometimes" appear to be elongated. And when the writers try to present the traditional example of the Doppler effect, they don't say that the perceived pitch of a train whistle "often" changes as the train passes by.

• Page 25: "Galaxies near the edge of the universe are racing away from the center of the universe at tremendous speeds. Galaxies closer to the center are also moving outward, but at slower speeds." So the writers evidently think that galaxies are scattering like the debris from a bomb that has exploded within a fixed space. That is all wrong. The universe has no "edge" and no "center." Space itself is expanding in all directions and is taking the galaxies with it -- and because there is no center, the expansion looks the same from all perspectives. This is a difficult concept to describe. Describing it only become harder if textbook-writers mislead students by comparing the universe to a bomb in a box.

• On page 27: "In a closed universe, a big bang may occur once every 80 to 100 billion years." That is pure speculation. We do not understand the Big Bang well enough to be sure that it would recur in a closed universe, let alone knowing how to estimate the interval between recurrences.

• On page 29: "Many [of the medium-sized] stars are very bright. Sirius, for example, is about twice the diameter of the sun and is the brightest star in the night sky." Sirius appears bright because it is nearby, not because it is intrinsically "very bright."

• On page 29 the Sun's diameter is stated correctly as 1.392 million kilometers, but on page 38 the diameter is said to be 1.35 million kilometers. Didn't anyone at Prentice Hall notice the inconsistency?

• Page 30, in a section about the sizes of stars: "Supergiants, however, pay a price for their huge size. They die off quickly and are the shortest-lived stars in the universe." The entire section about the sizes of stars is garbled. Stars can be meaningfully classified by their masses, but Prentice Hall's writers try to classify them by their diameters. This is meaningless because stars expand and shrink as they develop. Likewise, the writers don't understand that the term supergiant refers not to a particular kind of star but to a developmental stage through which many stars pass, even though the stars differ greatly in mass.

• Page 32, in the caption beside figure 1-24: "The brightness of these stars in the Trifid Nebula, as seen from Earth, is called absolute brightness." Figure 1-24 actually shows both the Trifid Nebula and the Lagoon Nebula, with the Lagoon Nebula at the center of the picture. And the definition given in the caption is incorrect. The brightness which we perceive when a star is seen from Earth is the star's apparent magnitude, not its "absolute brightness."

• Page 33: "The amount of light a star actually gives off is called its absolute magnitude." No, that's the star's absolute luminosity. The star's absolute magnitude is the magnitude that it would display if it were placed at a standard distance from Earth.

• Page 33: Here the student learns that "The relationship between the absolute magnitude and the surface temperature is shown in shown in Figure 1-25 . . . . This pattern forms the Hertzsprung-Russell (H-R) diagram." That statement is exactly backward. The diagram isn't formed by the pattern. The pattern emerges after we make the diagram.

• Page 36: "Astronomers measure the amount of red shift in a star's spectrum and use complex formulas to calculate how far from Earth a star is located. This method of calculating star distances is controversial, and not all scientists agree as to just how far away many stars are from Earth." Just what is "controversial" here? Is there disagreement about whether the amount of red shift is related to distance? Disagreement about the formulas used in performing the calculations? Disagreement about the accuracy of the calculated results? The writers' use of "controversial" explains nothing but has the effect of blurring the science that is under discussion.

• Page 42: "But periods of very active sunspot activity seem to occur every ten to eleven years." Why have the writers watered this down with the word "seem"? Periods of unusually vigorous sunspot activity do occur every ten to eleven years. It's a fact.

• Page 43: "According to the present theory of star evolution, the many different kinds of stars in the sky represent the various stages in the life cycle of a star." Wrong. Stars pass through stages during their lifetimes, but not every star passes through every stage or becomes "the many different kinds of stars in the sky."

• Page 44: "When the temperature within the [cloud of hydrogen atoms] reaches about 15,000,000º C, nuclear fusion begins. The great heat given off during nuclear fusion causes a new star, or protostar, to form. As a result of nuclear fusion, the protostar soon begins to shine and give off heat and light. At that point, a star is born." Rather than listing all the errors in that disastrous passage, I will rewrite the passage and state the facts accurately:

  As the spinning cloud collapses under its own gravity, its temperature rises. This hot, collapsing cloud is called a protostar. When the temperature at the core of the protostar reaches 15,000,000º C or so, nuclear fusion begins. The energy released during fusion flows outward, toward the protostar's surface. When it reaches the surface, there are sudden increases in the protostar's emissions of heat and light. At that point, a star is born.

• Page 46: "By the time most of the nuclear fusion in a massive star stops, the central core is mainly iron. Although the process is not well understood, the iron atoms begin to absorb energy. Soon this energy is released, as the star breaks apart in a tremendous explosion called a supernova." What? If those iron atoms absorb energy, where does the energy come from? Why is it later released? It is clear that Prentice Hall's writers do not understand the process that they are trying to write about.

• Page 47: "Neutron stars spin very rapidly. As a neutron star spins, it may give off energy in the form of radio waves. Usually the radio waves are given off as pulses of energy. Astronomers can detect these pulses of radio waves if the pulses are directed toward the Earth. Neutron stars that give off pulses of radio waves are called pulsars." This attempt to describe pulsars is entirely wrong. Neutron stars emit radiation continuously, not in pulses. In the case of a pulsar, the emitted radiation forms a beam. Each time the star rotates, the beam briefly crosses our line of sight and then passes out of view. As a result, the star appears to be emitting radiation in pulses -- but this is just an illusion.

• Page 68: "Billions of years ago, when the solar system was still forming . . . Venus may have been covered with planet-wide oceans. In fact, the remains of coastlines and sea beds can still be detected today." In fact, they can't. No such structures are discernible on Venus.

• Page 75: "A hundred Earths could be strung around Jupiter as if they were a necklace of pearls." According to a chart on pages 68 and 69 of Exploring the Universe, Jupiter's diameter is 142,700 km and Earth's diameter is 12,756 km. Using those numbers and some elementary geometry, we find that the number of Earths in the "necklace" would be about 38, not 100.

• Page 89: "The streak of light produced by a burning meteoroid is called a meteor. . . . A meteor that strikes Earth's surface is called a meteorite." So a meteorite must be a streak of light that hits Earth! The writers don't understand that a meteor is a meteoroid that has entered our atmosphere, and that meteors glow because they are hot (not because they are burning).

• Page 93: "Solid fuels [in rockets] burn rapidly and explosively. The pushing force that results is used up within seconds." The two solid-fuel rockets that boost the Space Shuttle burn for about two minutes. And how can a "force" be "used up"?

• Page 119: "Probably the most likely explanation for the origin of the moon is that the moon was 'born' when a giant asteroid the size of the planet Mars struck the early Earth, tearing a chunk of material from the planet. According to this theory, the Pacific Ocean may be the hole left when the moon was torn from the Earth." The idea that the Pacific Basin was formed in this way has not been taken seriously since the advent of plate tectonics in the early 1960s.

• Page 123: Here the writers say: "When the moon moves through the umbra, a total lunar eclipse occurs. When the moon moves through the penumbra, a partial lunar eclipse occurs." No. We see a partial lunar eclipse when a part of the Moon passes through the umbra.

• Page 13: "Thousands of years ago Arab shepherds discovered that about every three days a certain bright star suddenly became dim and disappeared, only to brighten again. In fear of this strange star, they named it Algol, the 'ghoul'." Algol is indeed a variable star that has a period of about three days, but all the rest of Prentice Hall's account is fiction. Every three days or so, Algol dims until it has lost about half of its brightness. This occurs not "suddenly" but slowly, over several hours, and Algol does not disappear. It stays visible throughout its cycle of dimming and resurgence. Though the name Algol is ancient and comes from Arabic, there is no record to suggest that any ancient Arabs noticed that this star was variable, or that they called it "the ghoul" to commemorate its variability. The notion that the people who named the star were specifically "Arab shepherds" -- not Arab explorers or Arab seamen or even Arab astronomers -- is pseudohistorical nonsense. (The first record of Algol's variability was produced in 1669 by an Italian professor of mathematics.)

• On page 28: "The German philosopher Nietzsche went mad because he believed that he had already taken every action he took." Huh? Nietzsche went mad because he was dying of syphilis. And there is no reason, to begin with, for dragging Nietzsche into a middle-school astronomy book.

• Page 66: "In 1975, two Soviet spacecraft (Venera 9 and Venera 10) landed on Venus. The spacecraft were not able to withstand the harsh conditions and functioned for only a few hours." In reality, Venera 9 lasted for 53 minutes, Venera 10 for 65.

• Page 83, in a passage about the discovery of Neptune: "It was located exactly where both Adams and Leverrier had predicted [it] would be." This cannot be correct. After astronomers noticed anomalies in the orbit of Uranus and inferred that the anomalies were caused by some unknown massive object, Adams and Leverrier independently calculated the object's location. Their results differed. But Prentice Hall's writers have incorrectly guessed that the location predicted by Adams was identical to the location predicted by Leverrier, and that this is "exactly" where the massive object (which we now call Neptune) was found. In fact, neither man's prediction was "exactly" right, though both predictions were good approximations.

• Page 85: "In the early 1900s, astronomer Percival Lowell . . . suggested that there was another planet whose gravity was pulling on both Neptune and Uranus. In 1930, after an intense search, a young astronomy assistant named Clyde Tombaugh found the ninth planet near where Lowell had predicted it would be." This is historically inaccurate and full of false implications. Percival Lowell predicted several locations (not just one) for the ninth planet, and these locations were spaced widely around the sky. Clyde Tombaugh didn't search for a ninth planet by pointing his telescope at the locations predicted by Lowell. Rather, he searched the part of the sky where, because of the motion of Earth, a ninth planet could be noticed most easily.

• Page 95: Here the writers say that the landings of Viking 1 and Viking 2 on Mars both occurred in 1975 and were "the first time [sic] spacecraft ever landed on another planet." Here are the facts. The first vehicle that landed on another planet and sent scientific data to Earth was the Soviet Union's Venera 7, which landed on Venus in December 1970. The first landing on Mars was achieved in December 1971 by Mars 3, but that vehicle's scientific apparatus failed after 20 seconds. The two Viking probes reached Mars in 1976, not 1975.

• Page 118: "Then the Lunar Orbiter space probe photographed the far side of the moon for the first time." Lunar Orbiter began to photograph the Moon in August 1966. The first photo of the far side of the Moon had been taken in October of 1959 by the Soviet Union's space probe Luna 3.

• Page 21: Here a half-page feature article plugs astrology, promotes the confusion of astronomy with astrological superstitions, teaches pseudohistorical fictions, and ends by asking: "Under what sign were you born? Do you know how your emotions are supposed to be affected by your sign?" Prentice Hall has been plugging astrology in this way for several years. The same article has appeared in earlier versions of Exploring the Universe and in Prentice Hall Exploring Earth Science [see note 1, below].

• Page 74, in a description of an imaginary voyage through the solar system: "Although you have had to steer your ship carefully, you have managed to pass safely through the asteroid belt." Traveling safely though the asteroid belt would be easy, since most of the asteroid belt is empty space. The notion that it is jam-packed with flying rocks comes from science-fiction films. Prentice Hall reinforces that notion by displaying a ridiculous painting (figure 2-18) in which the asteroid belt is depicted as a dense field of interplanetary objects.

• Page 87 is dominated by a section titled "Planet X -- The Tenth Planet." The writers claim that we still cannot understand the observed movements of Uranus and Neptune, and that "something else" must be pulling on them. This may make a good story, but there is nothing to it [note 2].

• On page 97 the writers label Magellan "the first European to provide evidence that the Earth is a sphere." Come on! Magellan was responsible for the first circumnavigation of the world, but Europeans had known since classical times that Earth is spherical. The ancient Greeks not only had deduced Earth's shape from physical evidence [note 3] but also had made a reasonably accurate measurement of Earth's circumference. Moreover, this knowledge had been handed down over the centuries, and it was used by Columbus, Magellan and the other great mariners of the Age of Exploration. Yet Prentice Hall seems to be clinging to the myth that, until Columbus's day, Europeans believed Earth to be flat [note 4].

Prentice Hall has been using some of this defective content since the 1980s. To an alarming extent, Exploring the Universe is a repackaging of material that appeared in Prentice Hall's general-science book A Voyage of Discovery, issued in 1986. This is true even though the list of "authors" in Exploring the Universe is completely different from the list of "authors" in A Voyage of Discovery.

Exploring the Universe has an extensive table of contents, and the names of many key concepts are printed in boldface type within the book's text. If textbook-adoption committees look no farther than that, they probably will get the impression that the book covers its subject. The truth is that Exploring the Universe is so badly lacking in depth, and bears such a crushing weight of erroneous material, that trying to use it as a teaching text would be a waste of time and effort. This book should not be welcome in any classroom.

Editor's notes

1. For an analysis of the article, see the review of Prentice Hall Exploring Earth Science in The Textbook Letter, September-October 1996. [return to text]

2. Prentice Hall has printed similar misconceptions before. See Lawrence S. Lerner's review of Motion, Forces, and Energy (another volume in the Prentice Hall Science series) in The Textbook Letter, November-December 1992. [return to text]

3. This evidence included the observation that Earth's shadow, as cast onto the Moon during a lunar eclipse, is always round. If an object always casts a round shadow, regardless of how or from what direction the object is illuminated, then the object must be a sphere. [return to text]

4. To read about another case in which Prentice Hall has promoted the flat-Earth myth, see the review of Prentice Hall Earth Science in The Textbook Letter, January-February 1992. For a brief account of how the myth originated, see "The Flat-Earth Story -- Again" in The Textbook Letter, March-April 1998. [return to text]

5. To read about a case in which Prentice Hall editors undoubtedly and undeniably reprinted material that they knew to be wrong, see the review of Prentice Hall Exploring Physical Science in The Textbook Letter for September-October 1995. [return to text]

Leonard Tramiel, of Palo Alto, California, is a computer programmer and an amateur astronomer. He holds a doctorate in astrophysics from Columbia University. He teaches astronomy in local schools, as a volunteer, under the auspices of Project Astro, sponsored by the Astronomical Society of the Pacific.

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