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APPROACHThere are many astronomy textbooks available today, but Pathways to Astronomy offers something different. . . .

Created by two veteran teachers of astronomy, both recipients of outstanding teaching awards, Pathways breaks down introductory astronomy into its compo-nent parts. The huge and fascinating field of astronomy is divided into 86 Units from which you can selectively choose topics according to your interests, while maintaining a natural flow of presentation.

One of the frustrations created by other current astronomy textbooks is that each chapter covers such a wide array of topics that it is difficult for students to absorb the large amount of material, and the texts are wed to such a specific order of presentation that it is difficult for the professor to link the chapter read-ings and review questions to his or her own particular approach to teaching the subject. Whether you are learning astronomy for the first time or teaching it for the tenth, Pathways offers greater flexibility for exploring astronomy in the way you want to.

The Unit structure allows the new learner and the veteran professor to relate the text more clearly to college lectures. Each Unit is small enough to be easily tackled on its own or read as an adjunct to the classroom lecture. For the faculty member who is designing a course to relate to current events in astronomy or a particular theme, the structure of Pathways makes it easier to assign reading and worked problems that are relevant to each topic. For the student of astronomy, Pathways makes it easier to digest each topic and to clearly relate each Unit to lecture material.

Each Unit of Pathways to Astronomy is like a mini-lecture on a single topic or closely related set of ideas. The same material covered in other introductory astronomy texts is included, but it is broken up into smaller, self-contained parts. This gives greater flex-ibility in selecting topics than is possible with the wide-ranging chapter in a traditional text that covers the same material as four or five Pathways Units.

Even though the Units are written to be as independent as possible, they still flow naturally from one to the next or even in alternative orders—differ-ent Pathways—through the book. Professors can select Units to fit their course needs and cover them in the order they prefer. They can choose individual Units that will be explored in lecture while assigning other Units for self-study. Or they can cover all the Units in full depth in a content-rich course. With the short length of Units, students can more easily digest the material covered in an indi-vidual Unit before moving on to the next Unit. And because the questions and problems are focused on a single topic, it is much easier to determine mastery of each topic.

Preface

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The Unit format also provides an opportunity to take some extra steps beyond the ordinary text. The authors have included some material of special interest that introduces topics most introductory texts do not offer—for example, Units on cal-endar systems and special relativity. More advanced material within a particular Unit topic is also organized toward the end of the Unit so that the essentials are covered first—also providing flexibility for assigning readings.

Pathways to Astronomy makes it easy to tailor readings and exercises so they fit best within a course’s structure. It also provides opportunities to travel down some fascinating paths to enhance a course or to provide additional reading for advanced students.

NEW TO THE FOURTH EDITIONNew Book Elements In our efforts to help students understand and interpret this wide-ranging material, we have added several new elements to Pathways:

Learning Objectives: At the start of each Unit, a new list of learning objectives describes the most important skills and abilities that readers should strive for in studying that Unit. These identify specific actions (such as describing, explaining, comparing, and calculating) that demonstrate a good mastery of the material.

Mathematical Insights: These marginal notes provide mathematical details to clarify the discussion in the text or expand beyond it, and they provide worked examples of mathematical problems.

New map format: We have converted almost every global map of the Earth, Moon, and planets to a Mollweide equal-area projection. Data are frequently released in a wide variety of projections, which introduce different distortions. Repro-cessing the data into a single format facilitates comparisons between planets, and the equal-area projection avoids distortions that exaggerate sizes in polar regions.

Mathematical Insight

New boxes in the margins explore the mathematics of the text more deeply

These marginal notes identify objects related to the text that can be seen in the Looking Up images at the front of the book —or with a small telescope.

LO O K I N G U P

Aphrodite Terra

Ishtar Terra

MaxwellMontes

AtalantaPlanitia

LaviniaPlanitia

Guinevere Planitia

Sedna Planitia

Aino Planitia

AlphaRegio

Atla Regio

Lada Terra

LakshmiPlanum

Maat Mons

BetaRegio

+8 km0 km−8 km

Elevation

Idunn Mons

Niobe Planitia

Looking Up Icons: These marginal notes point out objects that can be seen in the Looking Up pages at the front of the book, helping to relate the textual descrip-tions to objects visible in the night sky.

End-of-Unit questions: We have revised and added new questions to each Unit.

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Highlights of Changes In addition to our own monitoring of new and interesting results in the field, many readers and reviewers offered excellent suggestions for updates and improvements to Pathways. In all, more than 150 figures were added, updated, or replaced throughout the book to improve clarity and to include some of the best new images available. The Unit topics remain the same as the third edition, although a few Units were more extensively revised as noted below. The following is a partial list of changes, including the most interesting updates and additions:Unit 4 Foundations of Astronomy: Revised text and new figures for particles and

forces, with brief discussion of the Higgs particle. Unit 6 The Year: Revised discussion of seasons, and added figures of the Karnak

temple in Egypt and path of Sun as seen from different latitudes. Unit 8 Lunar Cycles: Revised eclipse text and figures and new eclipse-path map. Unit 10 Geometry of the Earth, Moon, and Sun: New figures illustrating Earth’s

curvature and ancient ideas of parallax. Unit 19 Tides: Revised figures to clarify tidal interactions. Unit 22 The Electromagnetic Spectrum: New figure with a multiwavelength

comparison of M31. Unit 23 Thermal Radiation: New figures with graphs illustrating the Wien and

Stefan-Boltzmann Laws. Unit 32 The Earth’s Atmosphere and Space: New figures and images of atmo-

spheric refraction. Unit 33 Amateur Astronomy: Updated images and discussion of amateur astro-

nomical photography. Unit 34 The Structure of the Solar System: Revised discussion and table of chem-

ical compositions in Solar System. Unit 35 The Origin of the Solar System: Added graph of radioactive decay. Unit 36 Other Planetary Systems: Extensively revised with new figures to illus-

trate exoplanet detection methods, planet migration, density determinations, and recent Kepler findings.

Unit 37 The Earth as a Terrestrial Planet: New figures and expanded discussion in section 3 on tectonics.

Unit 38 Earth’s Atmosphere and Hydrosphere: Revised figures and text on Cori-olis effect (section 5).

Unit 39 Our Moon: Reorganized section order, beginning now with the Moon’s formation. Many new figures and images from LRO and Lunar Prospector.

Unit 41 Venus: Added recent findings from Venus Express, and reprocessed imag-ery from Magellan.

Unit 42 Mars: Unit extensively updated and reorganized, adding several new and reprocessed images, for clearer development. Early results and images from Curiosity included.

Unit 43 Asteroids: New comparison images including Vesta results from Dawn. Unit 47 Satellite Systems and Rings: New Cassini images of Enceladus and

rings. Unit 49 Comets: Unit reorganized for clearer development with several revised

diagrams and new images from Stardust and STEREO. Unit 50 Impacts on Earth: Added Images from the Chelyabinsk meteor explosion. Unit 51 The Sun, Our Star: New diagram of Voyagers nearing interstellar boundary. Unit 54 Surveying the Stars: New image and discussion of finding Sun’s distance

from the transit of Venus. Unit 59 The H-R Diagram: Some details removed from H-R diagrams to make

them easier to understand. Unit 68 Neutron Stars: Updated discussion of recent observations of nearby neu-

tron stars and implications for their internal structure.

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M51The Whirlpool Galaxy can be seen as a dim patch of light with a small telescope. M51 is about 37 million ly away from Earth (Unit 76).

170,000 ly

Mizar and AlcorIf you look closely at it, you may notice that the middle star in the “handle” is actually two stars — Mizar and Alcor. Despite appearing close together in the sky, they are probably not in orbit around each other. However, with a small telescope, you can see that Mizar (the brighter of the star pair) has a faint companion star. This companion does in fact orbit Mizar. Moreover, each of Mizar‘s stars is itself a binary star, making Mizar a quadruple system (Unit 57).

Polaris

Little Dipper

Poin

ter s

tars

Big Dipper

Circling in the northern sky is the Big Dipper, part of the well-known constellation Ursa Major, the Big Bear. The Big Dipper is technically not a constellation, but just an asterism — a star grouping. It is easy to see in the early evening looking north from mid-March through mid-September. The Big Dipper can help you find the North Star, and with a telescope on a dark, clear night, you can find several other intriguing objects as shown below.

M97 — The Owl This planetary nebula (Unit 65) is ~2500 ly away.

~1.6 ly

Location of the Hubble Deep Field(Unit76)

Over the course of a night, stars appear to rotate counterclockwise around the star Polaris, which remains nearly stationary because it lies almost directly above Earth’s North Pole. Polaris is not especially bright, but you can easily find Polaris by extending a line from the two stars at the end of the bowl of the Big Dipper, the pointer stars, as shown by the dashed yellow line (Unit 13).

Big Dipper in 3-D

1 light year (ly) ≈ 10 trillion km ≈ 6 trillion miles

Earth

80 ly123 ly

83 ly80 ly

104 ly86 ly

83 ly

Ursa MajorLooking Up #2

xxviii Preface

Unit 69 Black Holes: New section on Hawking radiation. Unit 70 Star Clusters: New images of clusters showing them to the same scale. Unit 74 Mass and Motions in the Milky Way: Added Fermi observations of

gamma-ray bubbles and updated observations of orbits around central black hole.

Unit 79 Dark Matter: Added discussion of recent possible WIMP detections. Unit 80 Cosmology: New image and discussion of tentative detections of galaxies

at redshift greater than 10. Unit 84 Dark Energy and the Fate of the Universe: New diagrams and updated

cosmological parameters with results from Planck. Unit 85 Astrobiology: Updated with recent microfossil findings. Unit 86 The Search for Life Elsewhere: Added early Curiosity findings on Mars.

FEATURESLooking Up Illustrations It can be challenging to link introductory astronomy to the sky around us. The nine “Looking Up” full-page art pieces at the front of the book provide another pathway to astronomy, connecting what we actually see when “looking up” at the night sky with the more theoretical side of astron-omy. Each illustration displays a large-scale photograph of one or more constel-

lations in the night sky. Each also contains close-up photographs and illustrations of some of the most interesting telescopic objects with cross-references to the text. Details are also given regarding the objects’ distances from Earth, along with three- dimensional illustrations of some of the stars or other objects within the field of view. The Looking Up Illustrations begin on page ii, to make them easier to find.

Star Chart A good star chart also helps link the study of astronomy to the night sky. Pathways to Astronomy offers a foldout star chart as well as seasonal star charts for Northern Hemisphere observers. These will help students to take that next step beyond the book—exploring the night sky.

Detailed Art Pathways to Astronomy has taken each illustration a step further than the norm. Many fig-ures are annotated to describe the processes depicted within the illustration. Photos are often inserted next to the illustration for comparison so students can see the process in reality.

End-of-Unit Material The end-of-unit sections include hundreds of Key Points, Review Questions, Quantitative Problems, and Test Yourself questions to help students master the unit material. These ele-ments allow students to apply what they have learned before moving on to another unit. The answers for all the Test Yourself questions are provided at the back of the text.

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Clarification Points Marginal notes call attention to common misunderstand-ings that many people new to astronomy may have. These are points of confusion that seem particularly difficult to overcome, so they deserve special attention.

Concept Questions Dozens of Concept Questions are scattered throughout the margins of the units. These questions are designed to invite students to think beyond the text, and to think about questions that have no easy answer. Many also make good discussion questions in class.

Mathematical Symbols To help students work with the math and avoid confu-sion, throughout the text we have chosen unique symbols for each physical quan-tity and used them consistently. Where tradition dictates that the same letter be used for different quantities (such as acceleration and semimajor axis), we have used distinctive fonts. A symbol glossary is included at the start of the glossary to help students keep track of the meaning of symbols in formulas.

Cosmic Periodic Table We have produced a periodic table geared toward astron-omy. It is introduced in Unit 4 as part of the discussion of elements. This table is designed to convey information of interest to astronomers, such as relative abun-dances, condensation temperatures, mass excess (relative to iron-56), origins of elements, and radioactive lifetimes of unstable elements.The table has been revised with properties and names for some recently-measured elements.

Electronic Media Integration with the Text Icons for Interactives and Animations have been placed where additional understanding can be gained through an anima-tion or interactive experience.

Interactives McGraw-Hill is proud to bring you an assortment of 23 outstanding Interactives like no other. Each Interactive is programmed in Flash for a stronger visual appeal. These Interactives offer a fresh, dynamic method to teach astron-omy basics. Each Interactive allows users to manipulate parameters and gain a better understanding of topics such as blackbody radiation, the Bohr model, a “solar system builder,” retrograde motion, cosmology, and the H-R diagram by watching the effects of these manipulations. Each Interactive includes an analysis tool (interactive model), a tutorial describing its function, content describing its principal themes, related exercises, and solutions to the exercises. Users can jump between these exercises and analysis tools with just a mouse click.

Some widely held beliefs about astron-omy are known to be incorrect.

Clarification Point

I N T E R AC T I V E

A N I M AT I O N

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LEARNING RESOURCES

McGraw-Hill ConnectPlus®Astronomy provides online presentation, assignment, and assessment solutions. It connects your students with the tools and resources they’ll need to achieve suc-cess. With Connect Astronomy, you can deliver assignments, quizzes, and tests online. A robust set of questions and problems are presented and aligned with the textbook’s learning goals. As an instructor, you can edit existing questions and author entirely new problems. Track individual student performance—by ques-tion, assignment, or in relation to the class overall—with detailed grade reports. Integrate grade reports easily with Learning Management Systems (LMS) such as WebCT and Blackboard—and much more. ConnectPlus Astronomy provides students with all the advantages of Connect Astronomy, plus 24/7 online access to an eBook. This media-rich version of the book is available through the McGraw-Hill Connect platform and allows seamless integration of text, media, and assess-ments. To learn more, visit www.mcgrawhillconnect.com.

McGraw-Hill LearnSmart™McGraw-Hill LearnSmart™ is available as a standalone product or as an inte-grated feature of McGraw-Hill Connect® Chemistry. It is an adaptive learning system designed to help students learn faster, study more efficiently, and retain more knowledge for greater success. LearnSmart assesses a student’s knowledge

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of course content through a series of adaptive questions. It pinpoints concepts the student does not understand and maps out a personalized study plan for success. This innovative study tool also has features that enable instructors to see exactly what students have accomplished and a built-in assessment tool for graded assign-ments. Visit the following site for a demonstration: www.mhlearnsmart.com

McGraw-Hill SmartBook™Powered by the intelligent and adaptive LearnSmart engine, SmartBook is the first and only continuously adaptive reading experience available today. Distinguishing what students know from what they don’t, and honing in on concepts they are most likely to forget, SmartBook personalizes content for each student. Reading is no longer a passive and linear experience but an engaging and dynamic one, where students are more likely to master and retain important concepts, coming to class better prepared.

SmartBook includes powerful reports that identify specific topics and learning objectives students need to study. These valuable reports also provide instructors insight into how students are progressing through textbook content and are useful for identifying class trends, focusing precious class time, providing personalized feedback to students, and tailoring assessment.

How does SmartBook work? Each SmartBook contains four components: Pre-view, Read, Practice, and Recharge. Starting with an initial preview of each chapter and key learning objectives, students read the material and are guided to topics over which they need the most practice based on their responses to a continuously adapting diagnostic. Read and practice continue until SmartBook directs students to recharge important material they are most likely to forget to ensure concept mastery and retention.

McGraw-Hill Create™With McGraw-Hill Create™, you can easily rearrange chapters, combine mate-rial from other content sources, and quickly upload content you have written, for example, your course syllabus or teaching notes. Find the content you need in Cre-ate by searching through thousands of leading McGraw-Hill textbooks. Arrange your book to fit your teaching style. Create even allows you to personalize your book’s appearance by selecting the cover and adding your name, school, and course information. Order a Create book and you’ll receive a complimentary print review copy in 3–5 business days or a complimentary electronic review copy (eComp) via

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e-mail in minutes. Go to www.mcgrawhillcreate.com today and register to expe-rience how McGraw-Hill Create empowers you to teach your students your way. www.mcgrawhillcreate.com

My Lectures—Tegrity®McGraw-Hill Tegrity® records and distributes your class lecture with just a click of a button. Students can view anytime/anywhere via computer, iPod, or mobile device. It indexes as it records your PowerPoint® presentations and anything shown on your computer so students can use keywords to find exactly what they want to study. Tegrity is available as an integrated feature of McGraw-Hill Connect® Chemistry and as a standalone.

Classroom Performance System and QuestionsThe Classroom Performance System (CPS) brings interactivity into the classroom or lecture hall. CPS is a wireless response system that gives an instructor immedi-ate feedback from every student in the class. Each CPS unit comes with up to 512 individual response pads and an appropriate number of corresponding receiver units. The wireless response pads are essentially remotes that are easy to use and engage students. The CPS system allows instructors to create their own questions or use the astronomy questions provided by McGraw-Hill.

For the Instructor

• Test Bank The electronic test bank offers a bank of questions that can be used for homework assignments or the preparation of exams. The test bank can be utilized to quickly create customized exams. It allows instructors to sort questions by format or level of difficulty; edit existing questions or add new ones; and scramble questions and answer keys for multiple versions of the same test.

• McGraw-Hill Presentation Tools Build instructional material wherever, whenever, and however you want! Accessed through Pathways Connect site, the Presentation Tools are an online digital library containing assets such as photos, artwork, animations, and other media types that can be used to create custom-ized lectures, visually enhanced tests and quizzes, compelling course websites, or attractive printed support materials. Assets are copyrighted by McGraw-Hill Higher Education, but they can be used by instructors for classroom purposes. The visual resources in this collection include: • Art Full-color digital files of all illustrations in the book can be readily

incorporated into lecture presentations, exams, or custom-made classroom materials. In addition, all files are preinserted into PowerPoint© slides for ease of lecture presentation.

• Photos The photos collection contains digital files of photographs from the text, which can be reproduced for multiple classroom uses.

• Animations and Interactives Numerous full-color animations and the astronomy interactives, illustrating important processes, are also provided. Harness the visual impact of concepts in motion by importing these files into classroom presentations or online course materials.

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Also residing on your textbook’s Connect website are:

• PowerPoint Lecture Outlines Ready-made presentations that combine art and lecture notes are provided for each unit of the text.

• PowerPoint Slides For instructors who prefer to create their lectures from scratch, all illustrations and photos are preinserted by chapter into blank Pow-erPoint slides.

• Instructor’s Manual The Instructor’s Manual is housed within the Connect site and can be accessed only by instructors. This manual includes hints for teaching with this text, additional thought and discussion questions, answers to end-of-unit material, and sample syllabi.

ACKNOWLEDGMENTS Writing and revising a text such as Pathways is a collaboration with everyone who reads or uses it. We are deeply grateful to everyone who offered a suggestion, pointed out a mistake, or found a place where we might improve the content. Our sincere thanks to all the reviewers who have offered suggestions throughout the life of this book, especially those who offered their feedback in preparation of this fourth edition:

Lloyd Black Rowan UniversityMiles Blanton Bowling Green State UniversityPaul Butterworth George Washington UniversityMicol Christopher Mt. San Antonio CollegeJames Cooney University of Central FloridaRobert Egler North Carolina State UniversityPaul Eskridge Minnesota State University–MankatoPhillip Flower Clemson UniversitySteven Furlanetto University of California–Los AngelesJanet Mclarty-Shroeder Cerritos CollegeMilan Mijic California State University–Los AngelesAnatoly Miroshnichenko University of North Carolina–GreensboroJon Pedicino College of the RedwoodsGlenn Tiede Bowling Green State UniversityJose Vazquez New York University

Special thanks to those who were instrumental in the preparation of LearnSmart and SmartBook for Pathways to Astronomy as well as to those who helped develop and enhance our online homework offerings in Connect.

Lara Arielle Phillips University of Notre DameKaren Castle, Diablo Valley CollegeHugh H. Crowl Bennington CollegeGregory Dolise, Harrisburg Area Community CollegeBeth Hufnagel Anne Arundel Community CollegePatrick L. Koehn Eastern Michigan UniversitySusanna Lomant, Georgia Perimeter CollegeThomas Pannuti, Morehead State UniversityChristopher Shope Harrisburg Area Community CollegeMichael D. Stage Mount Holyoke CollegeChristopher Taylor, California State University, Sacramento

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Finally, the authors would like to thank the team at McGraw-Hill for all their assis-tance with updating Pathways, including Lora Neyens, April Southwood, Carrie Burger, Tara McDermott, Derek Elgin, Mary Reeg, and Pat Steele. Thank you to Louis Rubbo who revised and added new end-of-unit material. Thanks particu-larly to Beth Berry for a close reading of the revised manuscript and many correc-tions and suggestions for improvement.

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