Arny/Explorations an Introduciton to Astronomy

Explorations an Introduction to Astronomy Thomas T. Arny

About the Book

When I began writing Explorations: An Introduction to Astronomy, many people asked me why I was writing an astronomy book. Much of my motivation comes from wanting to share my own sense of wonderment about the Universe. I hope that in an astronomy course students can get some sense of where they fit in the astronomical Universe-a sense of location in the cosmic landscape. I also hope that students will come away from such a course with a sense of the richness of the Universe. When we look around us on our own planet, we see incredible biodiversity. So too when we look at the heavens, we see incredible astrodiversity. Stars, moons, and planets are as strange, colorful, and wonderful as tropical butterflies. Finally, I hope that students will gain some appreciation of the methods by which such tiny beings as we are have learned so much about the Universe. Not just laboratory techniques, those methods are far more important in the process of learning: the steps by which we go from observation to hypothesis and then on to what we hope is understanding.

But why write your own astronomy book when so many already exist? Most of the current books have so much material that they are impossible to get through in a single semester, and much material is omitted. I therefore decided that my first goal was to make a book that was short. However, as I worked at it, I kept finding things that I didn't want to leave out, material such as calendars and history of astronomy. But how could I write a short book and still include such topics? The solution was to organize the book so that instructors and students could omit the unwanted sections without interrupting the flow of ideas. Thus, I placed a number of topics such as time keeping and exo-biology into Essays that may be easily skipped. I also tried to make the book short by limiting its scope. Rather than covering everything, I have tried to focus on only what at the time seemed to me the most important ideas.

Another goal I set myself was to give simple explanations of why things happen. Such explanations generally involve physical principles that are unfamiliar to non-science students. However many even very complicated physical ideas can be appreciated, if not fully understood, by their appeal to analogy or to similarities with everyday phenomena. For example, diffraction effects can be seen 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. By tying physical principles to everyday observations, many of the more abstract and remote ideas become more familiar. Thus I have used analogies heavily throughout the book, and I have designed the illustrations to make those analogies more concrete.

An additional aim throughout this text is to explain how astronomers know the many curious things they have learned about our Universe. Such explanations often require mathematics, and so I have included it wherever it is crucial to understanding a method of measurement, as in the use of the modified form of Kepler's third law to determine a star's mass or in Wien's law to measure its temperature. However, because math is so intimidating to so many students, I have tried to begin these discussions by introducing the essence of the calculations in everyday language. Thus if the student or instructor chooses to omit the math, it will not prevent an understanding of the basic idea involved. For example, Wien's law relates the temperature of a hot object to its color by a mathematical law. However, the consequences of the law can be seen in everyday life when we estimate how hot an electric stove burner is by the color it glows. Similarly, I have tried to work through the math problems step by step, explaining that terms must be cross-multiplied, and so forth.

As a final goal, I have set many of the modern discoveries in their historical context. I want to demonstrate that science is a dynamic process and that it is subject to controversy. Ideas are often not immediately accepted, and to appreciate those that scientists finally settle on, it helps to understand the arguments for the against as well as the train of reasoning that leads to the "accepted" answer. On this point I must digress and reveal my own amazement (and naivete´) at how many widely accepted ideas have such flimsy underpinnings and how many widely quoted values for astronomical quantities are very imperfectly known.

New To The Second Edition

During the past two years astronomers have made important and exciting discoveries: distant, young blue galaxies; a gamma-ray source apparently located in a dim galaxy; evidence that meteorites from Mars may contain fossil evidence of ancient life on that planet; and evidence of perhaps a dozen or so planets around distant stars. Even though many of these claims and discoveries remain controversial, I think students should have the chance to learn a little about them and the evidence that supports what in some cases are truly amazing claims. For that reason a second edition of Explorations seems appropriate. Even now, as this edition goes to press, further exciting discoveries are making news: oceans beneath Europa's crust? Consensus on the value of the Hubble Constant? a reconciliation between the age of the oldest stars and the age of the Universe? In any case, a new edition was needed.

In putting this second edition together I have made relatively few changes in the book's overall structure, scope, or approach. The two most obvious changes are (1) the merging of the Essays on telescopes and light in the atmosphere into a chapter on telescopes, and (2) the addition of six "Overviews" that preview the material in related chapter blocks. My goal in the overviews is to help students see how the material they will encounter in the following few chapters fits together, so that they can see the broader context of what they are learning. The overviews have relatively little text and lots of pictures. Through this visual material, students may better remember and understand the material.

In addition to these changes, I have updated ideas in several chapters. For example, I've emphasized what I believe to be a growing belief that comets and asteroidal material have delivered much of the gas that makes up the atmospheres of the inner planets. As another example, I've discussed the observations with the Hubble Space Telescope that have begun to alter our view of how galaxies form and evolve. Moreover, observations with Hubble and Hipparchos may at last be reconciling the discrepancy between the age of the Universe and the ages of its oldest stars. All these changes may well be premature, but I think they deserve mention in the new edition. In making changes, I have tried to preserve what students and professors have told me they liked about the first edition. Please let me know your reactions to these changes, so that this book can continue to be as useful as possible.

A final comment about the new edition involves the accompanying CD-ROM. I suspect that still relatively few students have access to this technology. However, enough do to persuade the editors to include simple animations of some of the ideas that are difficult to visualize in still art. These animations were made by Greg Holt and Carolyn Duffy at ArtScribe, and I want to thank them for their usual flair for bright, clear art. I also want to thank David Shaw of McGraw-Hill Higher Education, who designed and executed the CD-ROM. He did a fine job of a very difficult task in turning a book into a multimedia product.

New to the 2000 version

This revised 2000 version of Explorations: An Introduction to Astronomy includes new discoveries and numerous minor revisions. This version retains the same layout and pagination to reduce the need for major changes in syllabuses and assignments and to minimize confusion for students, who for economic reasons are still using the 2nd edition. It has therefore not been possible to make extensive changes. However, I have added material in Chapter 17 on the evidence for a cosmological constant and its implications. I have also added a section in Chapter 7 on the recent Mars orbiter and lander. This reprint has also allowed me to fix some errors pointed out by users and to incorporate some of their suggestions for improved wording. Finally, I have added some more recent references and additional problems at the end of many chapters. Thus, users will find a book similar to the one they have previously used, but updated and, I hope, improved.

About the Package

The 2000 edition of Explorations includes the following ancillaries:

A new, expanded Web site with a wide variety of textual and visual materials that supplement the text.

A full interactive version of the text on CD-ROM that includes some twenty animations of figures such as eclipses, retrograde motion, and phases of the Moon.

An updated Instructor's Manual and Test Bank that includes references to additional articles and books, lecture outlines, and syllabi for a variety of course formats. Many new questions have been added to each chapter of the Test Bank.

Computerized Test Banks, a Mac and a Windows version, updated with over a hundred new questions.

A set of transparency acetates.

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