Preface

Stars, Galaxies, and Planets is a restructured version of Explorations and is intended for instructors who wish to cover stars and galaxies before the Solar System. Much of the restructuring is obvious. For example, the material on stars, galaxies and cosmology has been shifted from chapters 11-17 to become chapters 5-11. This has entailed relatively little rewriting, because Explorations was designed from the start so that the Solar System and stellar/galactic material could be read nearly independently. However, material on convection, density, and properties of magnetic fields which were introduced in the Earth chapter in Explorations, had to be shifted to the Sun chapter, because that chapter precedes the Earth chapter in this book. I have also taken advantage of the opportunity to do some minor up-dating and to make a few clarifications in material.

Such a re-ordering of a book entails a substantial risk. I have looked hard for all phrases of the sort, "We saw in chapter..." or "We will see in Chapter...." If you spot places where I have missed such forward or back references, please let me know. Similarly, I believe I have found and changed all places where terms are first used to be sure they precede the places they are needed, but again, if you spot occurrences of terms before they are defined, please let me know so that I may correct them.

As for the preface to Stars, Galaxies, and Planets ... , I will simply repeat below what I wrote for Explorations....

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. Those methods are not just laboratory techniques. Far more important is 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 the 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 nonscience students. However, many even very complicated physical ideas can be appreciated, if not fully understood, by 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 and against them, 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 naiveté) at how many widely accepted ideas have such flimsy underpinnings and how many widely quoted values for astronomical quantities are very imperfectly known.

Special updates

In this First edition of Stars, Galaxies, and Planets, I have tried to include the areas in which substantial changes in our knowledge have occurred or where different ideas are emerging. These include:

• Migration of the giant planets within the Solar Nebula
• The shape of planetary nebulas
• Evidence from the cosmic microwave background that our Universe is flat
• Evidence for "recent" water flows on Mars
• Hypotheses for why Earth and Venus have such different surfaces
• The discovery of numerous brown dwarfs and low-temperature stars

A feature of this edition is an animation icon placed next to topic headings that have related animations on the CD-ROM and the On-Line Learning Center. In addition, a description of the animation is next to the icon. There are approximately 80 animations that will help bring each concept to life as each shows its special simulated physical phenomena.

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Learn more about this powerful third release at www.mhhe.com/solutions

Customize this text in print or in an electronic format to meet your exact course needs. Through McGraw-Hill's Primis Online simply select your desired chapters, preferred sequence, and supplement them with the many science items on our database. Visit www.mhhe.com/primis/online to begin today.

HOW TO STUDY WITH THIS BOOK

Learning anything requires a certain amount of work. You certainly don't expect to be able to pick up a guitar and play it without practice, nor do you expect to be able to jog 5 miles without working out regularly. Learning astronomy also requires some work. The steps below may help you learn material better and more easily.

In reading any assignment, begin by looking at the pictures. Turn the pages of the chapter and familiarize yourself with what the objects you will be reading about look like. Then read the introduction. Next, jump to the summary. Finally, start again and read the assigned material through. As you read, make notes of things you don't understand and ask your instructor or teaching assistant for clarification. For example, if you are puzzled about why eclipses don't happen every month, make a note. I would urge you not to highlight as you read. Making a few short notes is much more effective than highlighting whole paragraphs.

Look carefully at the pictures and diagrams. If the figure caption has a question in it, try to answer it. Make your own sketch of diagrams to be sure you understand what they represent.

In a first reading of a chapter, I'd suggest that if you are troubled by math, you should simply skip it for the time being. Be sure, however, to read the material leading into the math so you at least understand what is being dealt with. When you encounter a mathematical expression of a physical law, put in words what the law relates. For example, the law of gravity relates the force of gravity to the mass of the objects and their distance from each other.

If you encounter words or terms as you read that you don't know, look them up in the glossary or index. You are just wasting your time if you read a description of some object and you don't know what it is.

When you finish the assignment, try to answer the review questions. They are short and are designed to show you whether you have assimilated the basic factual material of the assignment. Try to do this without looking back into the chapter, but if you can't remember, look it up rather than skip over the question. You might find it helpful to get a pile of scratch paper and actually write out short answers to the questions.

Having read the material once, go back and try to work through the math parts. Then try a practice problem to see if you can work through the material on your own.

If you get stuck at any point, see your teaching assistant or professor for help. Don't be shy about asking questions. I wish someone had beaten this into my head earlier. Learning is a thousand times easier if you ask questions when you get stuck.

Throughout the book, I have also tried to convey some of my own enthusiasm for astronomy. Many astronomical objects are strikingly beautiful. Others conjure up a sense of amazement. To me, it is the ultimate wonder that within the Universe, life has formed that can contemplate the Universe and ask what it is about. Seeing a clear night sky spangled with stars is for me a nearly religious experience. And yet the beauty that I see and my sense of wonder are enriched even more by an appreciation of the complex processes that make the Universe work. I hope this book will similarly increase your appreciation of our Universe's wonders.

If while using this book you find mistakes or if you have suggestions about how to make it better, please let me know. Write me at the Astronomy Program, University of Massachusetts, Amherst, MA 01003-4525, USA. If you have access to e-mail, please let me know that way. My address is arny@nova.astro.umass.edu. I really want your feedback.

ASTRONOMY ON THE INTERNET

Over the last few years, many teachers and students have gained access to an exciting new astronomy resource: the Internet. Hundreds of scientists around the world have created picture galleries and accompanying explanations that can be read by any user with access to the Internet. All are available free with the click of a computer mouse. Moreover, no special computer expertise is needed.

To use this resource, get a computer account at your school on a machine that runs a browser such as Netscape or Microsoft Explorer. Check with your local computer guru about how to connect your personal computer to the network or go to your library or computer room and use one of the computers there that is already set up. Typically, you'll need about 10 minutes to learn how to use the system. It is time well spent, because the Internet has become one of the best ways to find out the latest news about astronomical discoveries (similar systems exist for many other disciplines and hobbies). It would be impossible to list all the sites: they number in the thousands and change daily. Using one of the search engines such as Yahoo or Google will allow you to type in a few words that describe what you are interested in, and in a minute or so, you may have literally hundreds of suggested addresses that you can go to by simply clicking your computer mouse.

To help you navigate the labyrinth of the Internet, sites covering material in each chapter are featured on the Stars, Galaxies, and Planets web site at www.mhhe.com/arny.

To help you get started, I've listed below a few addresses of general interest.

"Yahoo." An amazing collection of special-interest pages on many subjects, including academic fields, travel, and entertainment. It also has a very good list of astronomical sources, including the beginnings of an on-line introductory astronomy text.

www.yahoo.com/Science/Astronomy/

"Welcome to the Planets." Many pretty pictures, fact sheets on the planets and the other Solar System objects, and a glossary. Prepared by the Jet Propulsion Laboratory.

pds.jpl.nasa.gov/planets

"Views of the Solar System," by Calvin Hamilton. Excellent pictures, fact sheets, and glossary. Lots of links to other sites.

www.seds.org

"Astronomy Picture of the Day." This site features images from both professional and amateur astronomers. It is a good place to find new pictures from various space observatories and ground based instruments.

"Astronomy and Space." A site with diverse links, including a simulated view of Earth that shows what portion is lit at the time you are logged in and "Solar System Live," a program that shows the position of the planets with a simulated Solar System for a huge range of dates that you can enter.

fourmilab.ch/nav/topics/astrospace.html

Note: Most of these addresses will suggest links to many additional sources, thus creating a web of information. Hence the name, "worldwide web."

ACKNOWLEDGMENTS

I owe thanks to many people for their help in this book, both for Explorations and for this new one. Help came in the form of advice, pictures, information, encouragement, and improvements to my own understanding of things. I have pestered all of my colleagues in the Five College Astronomy Department and many of them in the Department of Physics and Astronomy. Neal Katz, Eric Linder, James Lowenthal, Mike Skrutskie, and Martin Weinberg, as neighbors down the hall, bore a disproportionate share of questions, and I owe them special thanks. Gene Golowich read over an early draft on inflationary cosmology and made valuable suggestions. I profited from many conversations with Ted Harrison, the late Ed Phinney (of the Classics Department), Peter Schloerb, and the late David Van Blerkom. Other people who contributed were Bill Bates and Rick Newton, who helped with setting up and taking pictures, and Linda Ray Arny, who helped me locate many references. I also want to thank Amy Lovell for her careful proofreading of the first edition.

Many readers have been kind enough to take the time to send me suggestions for ways to improve the text or to point out errors. They include Bill Dent, Bill Irvine, Daniel Jaffe, Susan Kleinmann, Lauren Likkel, Mesgun Sebahu, Ron Snell, Mark Stuckey, Gene Tademaru, and Steve Schneider. I particularly want to thank the following people for very detailed critiques of several sections: Eric Feigelson (who read and commented extensively on the telescope chapter), Wei Lee, Rainer Mauersberger, James O'Connell, Joel Weisberg, Richard White, and Ben Zellner.

I also wish to thank William R. Luebke, who revised the test bank that he had done for the second printing of the first edition of Explorations and improved it dramatically.

Many people at McGraw-Hill have helped immensely. I am very grateful to Jim Smith, who began the project and read the entire manuscript in its first draft, and Judy Hauck, who was the developmental editor for the first edition of Explorations and turned it into such a fine and attractive book, and Donata Dettbarn who took over as the developmental editor for the second edition of Explorations.

As always, I am indebted to many reviewers, adopters, and students for suggestions and for spotting typos. In putting this edition together, I want particularly to thank James F. Andrus and Jeff Lewis, who spotted some typos and suggested a number of clarifications. I also want to thank my colleague Daniel Wang for his patience in answering questions about high-energy astronomy. The many reviewers whose direct input has shaped the changes in this third edition are listed separately, and I am very grateful for their time, suggestions, and careful thought.

I am also grateful to the many scientists who have obtained such lovely images-for example, the spectacular HST image of NGC 4414 and the Trace satellite image of solar magnetic loops. I am also grateful to the many people at McGraw-Hill for their fine work in producing the book. These include Brian Loehr, the developmental editor; Susan Brusch, the project manager; Carrie Burger and Mary Reeg, who dealt with the new art; and Marilynn Taylor, the copy editor.

Although innumerable people have read the manuscript, any errors that remain are my responsibility. If you find mistakes, please let me know. I want to make Stars, Galaxies, and Planets-as error-free as possible.

I am also deeply appreciative of the lovely work done by Carolyn Duffy and Greg Holt of ArtScribe, who did the color figures for the book. They listened patiently to my suggestions and turned my ill-drawn scrawls into bright, clear drawings. Likewise, I want to thank Jay Hoagland for the margin sketches.

Others at McGraw-Hill who made major contributions include Lloyd Black, who offered many helpful comments and ideas for the 1996 update of Explorations; John Murdzek, the developmental editor for the update of Explorations, who suggested many improvements; and Donata Dettbarn who searched diligently and creatively for the many beautiful new pictures. For the second edition of Explorations, I want to thank Nick Murray for both his careful copyediting and for a number of important suggestions and clarifications.

Lisa Gottshalk in the sales office also deserves a special thank you for her enthusiasm. Finally, I want to thank the many sales representatives who sent me comments from adopters and potential users about points they felt needed fixing. Thank you all.

REVIEWERS

The following people have reviewed Explorations at various stages of its development. I very much appreciate their help, suggestions, and corrections. Any errors that remain are not their fault, but mine. Aaron Galonsky, Michigan State University Alex G. Smith, University of Florida Alexander Dickson, Seminole Community College Alexander Gurshtein, Mesa State College Andrew Harris, University of Maryland Andrew P. Odell, Northern Arizona University Benjamin de Mayo, West Georgia College Brian M. Patten, Harvard-Smithsonian Center for Astrophysics Bruce Balick, University of Washington, Seattle Bruno Gruber, Southern IIlinois University Carl Rosenzweig, Syracuse University Carolyn Mallory, Moorpark College Chris Mihos, Case Western Reserve University Dan Wilkins, University of Nebraska David J. Griffiths, Oregon State University Donald Foster, Wichita State University Donald Terndrup, Ohio State University Douglas M. Kelly, University of Arizona Douglas R. Ingram, Texas Christian University Edward M. Sion, Villanova University Eric Feigelson, The Pennsylvania State University George F. Spagna, Jr., Randolph-Macon College Gerald H. Newsom, Ohio State University Harry Houpis, Sierra College Heidi Hammel, Massachusetts Institute of Technology Heinrich Eichhorn, University of FloridaJ. Scott Shaw, University of Georgia Jack W. Sulentic, University of Alabama James Christopher Hunt, Prince George's Community College James Mackey, Harding University James Schombert, University of Oregon Jeffrey A. Brown, Washington State University Jeffrey Kuhn, Michigan State University Jess Dowdy, Abilene Christian University Joan P. S. Kowalski, George Mason University John Greg Hoessel, University of Wisconsin John K. Lawrence, California State University, Northridge John L. Safko, Sr., University of South Carolina John Wayne Wooten, Pensacola Junior College Jon K. Wooley, Eastern Michigan University Jonathan I. Lunine, University of Arizona Kristine Larsen, Central Connecticut State University Larry Sessions, Metropolitan State College of Denver Mark Edwards, Hofstra University Melvyn Oremland, Pace University Michael J. Bozack, Auburn University Michael Stewart, San Antonia College Milan Mijic, California State University, Los Angeles Nancy D. McDonald, Palm Beach Community College Norman L. Markworth, Stephen F. Austin State University Norman Sperling, Chabot Observatory and Science Center Panos Photinos, Southern Oregon UniversityPaul Nienaber, Marquette UniversityPeter O'Shull, Jr., Oklahoma State University Rahul Mehta, University of Central Arkansas Richard Rees, Westfield State College Robbie F. Kouri, Our Lady of the Lake University Robert A. Egler, North Carolina State University Robert Page, University of Maine at Augusta Scott B. Johnson, Idaho State University Tai L. Chow, California State University, Stanislaus Terry Jay Jones, University of Minnesota Thomas Christensen, University of Colorado at Colorado Springs Thomas Hockey, University of Northern Iowa Timothy Beers, Michigan State University Tom Balonek, Colgate UniversityW. C. Woods, Glassboro State CollegeW. R. Luebke, Modesto Junior College Walter Wesley, Moorehead State University Wendy Hagen Bauer, Wellesley College William C. Keel, University of Alabama William Seeley, Massachusetts College of Liberal Arts Yong H. Kim, Saddleback College

I am especially grateful for the very detailed and thoughtful comments and suggestions of Thomas Hockey, John Greg Hoessel, Terry Jay Jones, Norman Sperling, Virginia Trimble, and Dan Wilkins, and I want particularly to thank Eric Feigelson for his helpful and thoughtful suggestions for the first edition of Explorations.

ANCILLARY PACKAGE

This First edition of Explorations: Stars, Galaxies, and Planets has an impressive set of ancillary materials. They include:

An Essential Study Partner CD-ROM has study aids organized by topic. Each section includes animations modeling key concepts discussed in the book, practice quizzes, flashcards, and crossword puzzles using key terms and glossary definitions. Also included on the CD-ROM are guest essays written by professors that expose students to a different viewpoint on a topic or a new research project. This interactive resource is packaged free with each new textbook.

The Astronomy PowerWeb, linked to from the Arny On-Line Learning Center, is the first on-line supplement to offer students access to course-specific current articles referred by content experts; course-specific real-time news; weekly course updates; interactive exercises and assessment tools; study tips; web research tips and exercises; referred and updated research links; daily news; and access to the Northernlight.com Special Collection™ of journals and articles. A pass card is packaged free with each new textbook.

An OnLine Learning Center offering unlimited resources for both the student and the instructor is found at http://www.mhhe.com/arny. Instructors can access PowerPoint presentations, sample syllabi, an online instructor's manual, plus other on-line teaching tools. Students will be able to use an astronomy timeline, scorable practice quizzes, questions and problems, and more. By way of this text-specific web site, students and instructors will be better able to quickly incorporate the Internet into their classroom.

NetTutor offers students live, personalized tutoring via the Internet. Using NetTutor's powerful wwwhiteboard software, students can post a question and receive prompt feedback from an expert in their subject. The WWWhiteboard allows students and tutors to use proper mathematical notation as well as other highlighting features-truly making this a unique learning experience. Students may also post questions to the Q&A Center and receive a reply within 24 hours. Visiting the Message Center allows students to discuss difficult concepts among themselves, while the Archive Center provides a browseable list of questions and answers maintained by the subject tutor. NetTutor comes FREE with Explorations: Stars, Galaxies, and Planets, by Tom Arny, and is an invaluable aid for all students. It's the study partner who always has all of the answers.

An Instructor's Manual that includes references to additional articles and books, lecture outlines, and syllabi for a variety of course formats can be found on the Online Learning Center.

A Computerized Test Bank available for both Macintosh and Windows programs.

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