When I began Explorations: An Introduction to Astronomy, many people
asked me why I was writing an astronomy book when so many already
existed. In answering such questions, I found that I had many reasons,
ranging from the personal to the pedagogic. Part of my motivation came
from my sense of wonder about the Universe. The Universe is an amazing
place, and I wanted to convey some of my own wonderment to my
students.
As I began writing this book, I began to understand why the existing
textbooks were very long and overwhelming in detail. I kept finding
things that I didn’t want to leave out—such as calendars and the history of
astronomy. Moreover, reviewers kept suggesting things that I must
include, but rarely did they suggest things I could omit. This led me to
rethink how I wanted to organize Explorations. I covered some topics,
such as timekeeping and exobiology, in essays that the instructor might
choose to skip. Moreover, small duplications in material make it possible
to jump directly to some of the later chapters without having to work
through the details of all the earlier chapters.
Perhaps my main goal was to give simple explanations of why things
happen. Many astronomy books today seem to simply say “this is how it
is.” I wanted instead to offer explanations, drawing as much as possible on
simple, everyday effects that students can see around them in the world.
For example, why do some stars pulsate? A simple analogy of steam building
up pressure under the lid of a pan offers a model of this phenomena that
is easy to understand and reasonably accurate. I have also tried to link complex
physical processes to simple everyday experiences. For example, you
can see the effects of diffraction by looking at a bright light through a lock
of your hair pulled over your eyes or through glasses that you have fogged
with your breath. When we can thus link physical principles to everyday
observations, many of the more abstract and remote ideas become more
familiar. I have also used analogies heavily throughout the book, and I
have designed the illustrations to make those analogies more concrete.
Knowing the facts about astronomical objects is important, but it is
almost equally important to understand how astronomers deduce those
facts. Thus, an additional aim throughout this text is to explain how
astronomers have come to their understanding of our Universe. The
Science at Work boxes illustrate how observations may force astronomers
to revise their ideas of how a given process occurs. As part of showing how
science works, I have set many of the modern discoveries in their historical
context to illustrate that science is a dynamic process and subject to
controversy—many ideas are not immediately accepted, even if they
ultimately prove to be “correct.” I hope that by seeing the arguments for
and against various ideas, students will have a better understanding of
how science works. I myself am amazed at how many widely accepted ideas have such flimsy underpinnings and how many widely quoted values
for astronomical quantities are very imperfectly known.
I would be remiss not to mention the role of mathematics in science.
Math is essential for understanding a number of methods used by astronomers,
and I have therefore included some mathematics in a number
of places. However, because math is so intimidating to so many students,
I begin these discussions by introducing the essence of the calculation in
everyday language so that the basic idea can be understood without understanding
the mathematics. For example, Wien’s law relates the temperature
of a hot object to its color by a mathematical law. However, illustrations
of the law can be seen in everyday life when we estimate how
hot an electric stove burner is by the color of its glow. Where I present the
mathematics, I work through it step by step, explaining where terms must
be cross-multiplied and so forth.
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2006 McGraw-Hill Higher Education