iv
Contents
Who Is This Book For? 1
The Pedagogical Approach of The Essential Cosmic Perspective 1
Preparing Your Course: Suggestions for First-Time Astronomy Teachers 1
Suggestions on Making Your Lectures Interactive 15
Part I: Developing Perspective 21
Chapter 1 A Modern View of the Universe 22
Chapter 2 Discovering the Universe for Yourself 35
Chapter 3 The Science of Astronomy 47
Part II: Key Concepts for Astronomy 54
Chapter 4 Making Sense of the Universe: Understanding Motion,
Energy, and Gravity 55
Chapter 5 Light: The Cosmic Messenger 67
Part III: Learning from Other Worlds 79
Chapter 6 Formation of the Solar System 80
Chapter 7 Earth and the Terrestrial Worlds 92
Chapter 8 Jovian Planet Systems 105
Chapter 9 Asteroids, Comets, and Dwarf Planets: Their Nature,
Orbits, and Impacts 117
Part IV: Stars 138
Chapter 11 Our Star 139
Chapter 12 Surveying the Stars 151
Chapter 13 Star Stuff 164
Chapter 14 The Bizarre Stellar Graveyard 178
v
Part V: Galaxies and Beyond 190
Chapter 15 Our Galaxy 191
Chapter 16 A Universe of Galaxies 201
Chapter 17 The Birth of the Universe 214
Chapter 18 Dark Matter, Dark Energy, and the Fate of the Universe 226
Part VI: Life on Earth and Beyond 238
Instructor Guide for The Essential Cosmic Perspective, Eighth Edition 1
Who Is This Book For?
The Essential Cosmic Perspective is designed primarily for one-semester survey
courses in astronomy. We assume no prior knowledge of astronomy or physics,
and the book is especially suited to students who do not intend to major in
mathematics or science. We have tailored The Essential Cosmic Perspective to
one-semester survey courses by carefully selecting the most important topics in
The Pedagogical Approach of
The Essential Cosmic Perspective
We have built The Essential Cosmic Perspective around a carefully thought-out set
of themes and pedagogical principles, all laid out in the Preface of the textbook. If
you are new to teaching from our textbook, we believe you will find it useful to
familiarize yourself with these themes and principles, since understanding our
approach will make it easier for you to help your students get the most out of your
course.
Preparing Your Course:
Suggestions for First-Time Astronomy Teachers
If you’ve taught astronomy before, then you know how much work you must put
into course preparation in order for the course to run smoothly and seamlessly for
your students. This section is intended to help reduce that workload by giving you
What Is Teaching All About?
Forgive us for pontificating, but before we get into details of course preparation
we’d like to make a general point about teaching:
• This may sound strange, but if you think about it, you’ll realize that you
can’t “teach” anyone anything. The only way that any of us ever learn is
by learning for ourselves. Your job as a teacher is to make learning
possible. Simply trying to “pour” facts into students’ heads won’t work.
But if you motivate them, encourage them to work at learning, and answer
their questions, you will be a great teacher.
2 Bennett, Donahue, Schneider, Voit
General Notes on Course Preparation
The broad range of material covered in introductory astronomy courses can be
intimidating to teach, especially if your primary scientific training was not in
astronomy. (Note: A large fraction of the people teaching introductory astronomy
courses have degrees in physics rather than astronomy.) Here are a few general
suggestions that will help you stay ahead of your students and keep your course
running smoothly. We apologize if they seem obvious, but for some new
instructors they will be useful.
• Be Clear About Your Expectations of Students. Perhaps the single most
important thing you can do to help your students achieve success in science
is to lay out clearly what it takes for them to succeed in your class. Thus,
before your course begins, you should decide what you intend to ask of your
students—for example, how much homework you will assign (see p. 7,
when exams will be scheduled, whether work with MasteringAstronomy
tutorials is optional or required, and how you will determine final grades.
Once you have made your decisions, you should communicate them clearly
to students. This communication can be done in at least three ways:
◦ Prepare a syllabus that lays out all your expectations and grading
policies clearly. This syllabus can then serve as the single reference for
students whenever they have questions about class logistics or if they
• Read the Chapters and Try the Assignments You Give to Students.
Although it may seem obvious that you should do what you ask of your
students, we’ve found a depressingly large fraction of college professors
(across all subjects) who, for example, assign reading that they’ve never
read themselves or assign problems that they haven’t tried to solve
themselves. Clearly, you cannot anticipate student questions or understand
the problems they run into if you don’t know what they’ve been reading
and working on. Ideally, you would read all the assigned chapters before
your course begins. Realistically, as some of you may have very little prep
time available, you can succeed by skimming the chapters before the
course begins and reading them in depth a day or two ahead of when you
expect students to have read them.
Instructor Guide for The Essential Cosmic Perspective, Eighth Edition 3
• Try to Be Consistent with the Text (Especially with Jargon). Students
learn best when the reading, homework assignments, class lectures, and
discussions all reinforce one another. This is not to say that you cannot
deviate at all from the textbook presentation; it only means that you should
strive for as much consistency as possible and should make sure to let
students know when you choose to do things differently. For example:
◦ In many cases, it may work quite well if you present a topic in class in
a different way than we present it in the book or include a topic that
we don’t cover at all in the book. However, since students are
(hopefully) reading the book, it’s important that you let them know
when and why you are doing something differently, so that they don’t
become confused (e.g., asking themselves, “Who’s right, the book or
• Become Familiar with the Study Resources Available to Your
Students. No matter how well you teach or how good our book, many of
your students will still have difficulty in your course. Thus, one of your
most important jobs as a teacher is to help steer these students to resources
that will help them overcome their difficulties. Obviously, you cannot
steer them well unless you know what resources are available. In
particular, you should familiarize yourself with all of the following:
◦ The study resources on the MasteringAstronomy website, including
the tutorials, videos, and online quizzes. For many students, making
good use of these resources will be all they need to overcome their
difficulties with course material.
◦ Campus resources for students, such as tutoring centers, study skills
workshops, and counseling services. Most college campuses offer at
least some resources to help students who are having difficulty. Some
4 Bennett, Donahue, Schneider, Voit
• Stay Current with Astronomical News. Astronomy generates frequent
headlines in the news media, and we believe that a major goal of an
astronomy course should be to get students sufficiently interested in the
subject that they become lifelong followers of astronomical news. One of
the best ways you can generate this enthusiasm is to bring current
astronomical news into your class. You should follow the news closely for
reports of discoveries or missions that may be relevant to your class. It’s
well worth taking a few minutes out of your planned lecture to report on an
exciting new discovery, even if it’s in a different area of astronomy than the
• Share Resources and Ideas with Other Instructors. Just as your
students should never feel helpless when they run into difficulties, you
should never feel like you are alone as a teacher. There are lots of other
astronomy teachers out there with lots of great ideas, and there’s always
some way to share the load. For example:
◦ If you teach at a school where multiple instructors are teaching the
same course from the same textbook, try to share resources, teaching
ideas, and plans for homework assignments or exams. If possible, hold
Setting Your Grading Policy
A key part of setting student expectations is making sure that you have a clearly
stated grading policy. Setting such a policy can be more difficult than it sounds,
and the policy you set depends in part on the time you have available for grading
students’ work. Nevertheless, as a general guideline, we recommend basing
grades on some combination of the following:
1. Homework sets consisting of selections from the end-of-chapter problems
and assignable work from the tutorials on the MasteringAstronomy website.
We generally recommend scheduling homework on a regular basis, such as
2. Some set of quizzes and/or exams; for example, you might choose short
3. One or more projects, selected from the Web projects or some of the
research questions that appear in the end-of-chapter exercise sets.
Note: Be very clear about your policy regarding late assignments and make-
ups. For a large class, you may wish to set a policy of “no make–ups” on
Weighting the Components of the Final Grade
Once you decide what to assign, you must assign a weight to each component in the
final grade. Again, the weight will depend on your personal style and resources for
grading. However, we have some opinions that we’ll now share with you.
• In science courses, we have a tendency to base grades strictly on content
knowledge. For example, in a physics course for majors, those who can
solve the problems get high grades and those who can’t get low grades.
However, we believe that in a course for nonscience majors, grades should
reflect effort at least as much as content knowledge. The reason is simple:
Because an introductory astronomy course has no prerequisites, students
enter with a wide range of prior content knowledge. Thus, if you base your
grades strictly on content knowledge, you may effectively be grading
students as much on what they knew before your course as you are on
6 Bennett, Donahue, Schneider, Voit
• The best way to reward effort is to make homework and projects count as
a substantial fraction of the final grade. This is particularly true of essay-
type questions, which require students to write clearly and demonstrate an
ability to defend their answers, as opposed to simply getting an answer
The Grading Scale
The primary question in setting a grading scale is whether to use a curve or a
“straight” scale. There’s really no right answer to this question, but our own
preferences lean toward a straight scale for one key reason: We feel an obligation
to combat the rampant grade inflation on college campuses. With a curve, it’s too
easy to succumb to student pressure (and these days parent pressure, too) and
decide that “average” should be a B or an A– rather than a C. In contrast, if you
set a policy that a weighted average of 90% on all assignments constitutes an A–,
it is very difficult for anyone to argue with you.
An added advantage of the straight grading scale is that it allows you to tell the
students straight-faced (no pun intended) that you are willing to give each and every
Instructor Guide for The Essential Cosmic Perspective, Eighth Edition 7
Setting Your Homework Policy
As discussed above, we suggest assigning at least some homework unless a lack
of grading resources makes it completely impossible. The key issue is deciding
precisely what and how much to assign. You have a lot of choices. The book
alone has far more end-of-chapter problems than you could reasonably assign to
your students, and on top of that you have the option of assignments based on
MasteringAstronomy. A good way to decide what to assign is to read through the
various problems and projects and then choose the ones you’d like to emphasize.
When selecting particular problems for assignment, you may wish to consider the
following:
• The “How to Succeed” section in the textbook’s Preface recommends that
students in a 3-credit class should expect to spend about 2 to 3 hours per
week on homework (i.e., on working problems, not counting time for
• We recommend a mix of easier and harder problems, as well as a mix of
problem types. For example, from a particular chapter you might assign a
few problems from the end-of-chapter exercises, one of the
MasteringAstronomy online quizzes, and a few selections from the
Selective Homework Grading
How are you going to grade all that homework? This is one of the most
challenging questions in teaching, since we rarely have enough resources to grade
all the work that we’d like to assign. One option, of course, is to assign only
problems that can be automatically graded with the MasteringAstronomy website.
We now have a library with hundreds of exercises (called “tutorials” on the site)
in this category, making it a viable option.
8 Bennett, Donahue, Schneider, Voit
If you choose to assign exercises that require someone actually looking at
them—such as short answer or essay questions, or quantitative problems in which
you must follow student work—we recommend a selective grading strategy. That
way students still get the benefit of the learning that homework entails (and
homework really is the best way to learn), while you are able to assign grades in a
practical and fair way. Our recommended strategy goes like this:
• Tell students in advance that you will grade only a few of the problems that
• In addition to grading a few problems in detail on each assignment, also
assign part of the grade based on a skim of the homework’s completeness
and presentation. A quick scan is usually all you need to figure out who
really put in effort and did a good job and who didn’t. For example, if you
say that a homework assignment is worth 10 points, reserve 2 points for this
overall “presentation” score while grading 4 other problems for 2 points
each. (On a 10-point homework scale, we usually award half-points as
needed; thus, the 2 points can essentially become 2, 1.5, 1, 0.5, or 0, which
correspond to A, B, C, D, and F.) While the 2 points for “presentation” may
seem rather small given that it actually represents most of the work the
students turned in (since you grade in detail only a small fraction of the
Homework Help
We encourage you to find ways to provide your students with plenty of
homework help on request. Again, because of the varying science backgrounds
of students in introductory courses, this is the only way to ensure that those with
Instructor Guide for The Essential Cosmic Perspective, Eighth Edition 9
help only if they have already tried the problems themselves. We go so far as to
tell students that, if necessary, we’ll lead them step-by-step through everything
they must do to write down a correct solution (in reality, it very rarely comes to
Setting Your Testing Policy
Studying for tests actually helps students consolidate their learning. Thus, it is a
good idea to give quizzes and exams even if you assign extensive homework.
Here, we discuss a few considerations that concern testing policy.
Multiple-Choice or Essay?
It’s widely acknowledged that short-answer or essay-type questions are a better
diagnostic of student understanding of particular concepts than are multiple-
choice questions. However, this advantage must be weighed against two
drawbacks to essay-type exams: (1) They take much longer to grade than
Should You Give Short Quizzes?
We have found that, because of the rapid pace at which students encounter new
concepts in astronomy courses, it is useful to give frequent quizzes. There are two
basic ways in which you can do this:
• Using MasteringAstronomy, you can receive scores when your students