from The Textbook Letter,
Reviewing a middle-school book in the Prentice Hall
Exploring the Universe
1997. 167 pages. ISBN of the student's edition: 0-13-423385-9.
Prentice Hall, 1 Lake Street, Upper Saddle River, New Jersey 07458.
(Prentice Hall is a part of Pearson Education. Pearson Education is
a part of Pearson PLC, a publishing company based in London.)
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.
I first encountered Prentice Hall's book Exploring the
Universe when, as a volunteer teacher of astronomy, I visited a
classroom in a local middle school. I opened Exploring the
Universe to a random page, and I saw an error. Then I turned to
another page, and I saw another error. Then I went to the front of
the book, started to read systematically, and found many more
errors. At that point, I decided to read the whole book and write a
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.
Factual and Conceptual Failings
- 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
- 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
- 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
- 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
- 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
- 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
- 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
- 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
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
- 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
- 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
Besides teaching scientific "facts" that are false and
"explanations" that are false or meaningless, Exploring the
Universe makes false "historical" statements. For example:
- 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
- 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
- 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
- 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.
Affirming Myths and Pseudoscience
Prentice Hall's book is also degraded by passages in which the
writers promote pseudoscience and affirm popular myths:
- 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
Material from the 1980s
Exploring the Universe could be worse. In fact, it
was worse when it first was published, in 1993. I have read
the 1993 version, and I have noticed that it contained three
mistakes which now, in the 1997 book, have been corrected. Is it
reasonable to believe that those three were the only mistakes that
Prentice Hall's editors had learned about during four years? I
think not. I think that those three were very easy to fix, so the
editors fixed them -- while leaving all the rest of the book's
defective material in place
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.
- 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]
- 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]
- 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]
- 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]
- 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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