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Astronomy Journey to the Cosmic Frontier Sixth Edition John D. Fix University of Alabama in Huntsville ASTRONOMY: JOURNEY TO THE COSMIC FRONTIER, SIXTH EDITION Published by McGraw-Hill, a business unit of The McGraw-Hill Companies, Inc., 1221 Avenue of the Americas, New York, NY 10020. Copyright © 2011 by The McGraw-Hill Companies, Inc. All rights reserved. Previous editions 2008, 2006, 2004 (updated edition), 2001, 1999, and 1995. No part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written consent of The McGraw-Hill Companies, Inc., including, but not limited to, in any network or other electronic storage or transmission, or broadcast for distance learning. Some ancillaries, including electronic and print components, may not be available to customers outside the United States. This book is printed on recycled, acid-free paper containing 10% postconsumer waste. 1 2 3 4 5 6 7 8 9 0 WDQ/WDQ 10 9 8 7 6 5 4 3 2 1 0 ISBN 978–0–07–351218–1 MHID 0–07–351218–4 Vice President & Editor-in-Chief: Marty Lange Vice President EDP/Central Publishing Services: Kimberly Meriwether David Publisher: Ryan Blankenship Sponsoring Editor: Debra B. Hash Senior Marketing Manager: Lisa Nicks Senior Project Manager: Lisa A. Brufl odt Design Coordinator: Margarite Reynolds Senior Photo Research Coordinator: Lori Hancock USE Cover Image Credit: NASA, ESA, and the Hubble SM4 ERO Team Senior Production Supervisor: Sue Culbertson Compositor: S4Carlisle Publishing Services Typeface: 10.75/12 Garamond Printer: World Color/Dubuque All credits appearing on page or at the end of the book are considered to be an extension of the copyright page Library of Congress Cataloging-in-Publication Data Fix, John D. Astronomy : journey to the cosmic frontier / John D. Fix. – 6th ed. p. cm. Includes bibliographical references and index. ISBN 978-0-07-351218-1 1. Astronomy–Textbooks. I. Title. QB43.3.F59 2010 520--dc22 2009050731 www.mhhe.com For Cynthia Foreword A layman challenges astronomers with the assertion: “If experience than a supernova, a galaxy, the Big Bang, or a every object in the universe except the Earth, the Sun, and black hole? But these astronomical concepts have become the Moon were eliminated, most people wouldn’t know a part of popular culture and language. the difference.” There is, undeniably, a measure of truth Astronomy takes its place with art, music, literature, to this assertion. It resembles the assertion that humans drama, and religion as an inspiring subject in the minds are interested only in food, shelter, and procreation. But and hearts of sensitive and thoughtful individuals. It con- the full truth is much richer and more complex. Even the tributes to lifting the human spirit above the break-even most primitive peoples marvel at the dazzling beauty of level of bare survival. We would be much the poorer with- the night sky, identify stable patterns in the arrangement out it. Is astronomy of practical importance? In a restricted of easily identifi ed stars, and note the movement of a few sense, yes; it plays a key role in navigation, timekeeping, bright points of light, the planets, on the star fi eld. They and the manifestation of physical principles at work in also derive spiritual inspiration from this scene. More ad- complex systems. But the grandeur and enormous physi- vanced civilizations have shared this inspiration and gone cal scale of the universe and the realization of our tiny part beyond it to seek a scientifi c understanding of the grand in it are the aspects of astronomy that enrich our lives and scheme of the universe. permeate our culture. Even the most sophisticated modern astronomers are Join Professor Fix and his professional colleagues motivated by a primal awe of their subject. These astron- in this great intellectual adventure of exploration and omers then attempt rational explanations of its infi nite discovery. detail, piece by piece, and they carry along with them the whole or nearly the whole of humanity. For example, what James A. Van Allen could be more esoteric or more remote from everyday 1914–2006 v Preface As James Van Allen wrote in his foreword to this book, I would be grateful for any suggestions and advice for astronomy permeates our culture. Of all the sciences, improving this book. If you have any ideas to offer, please astronomy is the one that generates the most public contact me at the Department of Physics, University of interest. There are hundreds of thousands of amateur Alabama in Huntsville, Huntsville, Alabama, 35899, or astronomers, two monthly astronomy magazines with by e-mail at [email protected]. healthy circulation, and television specials about important astronomical discoveries. The demotion of What’s New? Pluto from planet to dwarf planet generated headlines and editorials around the world. Part of the public inter- Content Updates and Additions As stated, one est in astronomy is surely due to the dramatic scope of of the goals of this text is to keep students up to date on the science. Part, I am sure, is because nonprofession- current astronomical events and discoveries. In doing so, als not only can understand astronomical discoveries many new topics have been added to the sixth edition, and but also can make some of those discoveries. Ama- several topics from previous editions have been updated. teur astronomers regularly carry out important astro- Some of these include: nomical observations, often with telescopes they have made themselves. New Topics • Fermi gamma-ray telescope (Chapter 6) The Goals of Astronomy: • Recent Moon missions (Chapter 9) Journey to the Cosmic Frontier • Results from the Messenger mission to Mercury (Chapter 10) I wrote this book as a text for an introductory course in • The discovery of ice by the Phoenix Mars lander astronomy for college students. I have taught such a course (Chapter 11) for many years at the University of Iowa and the Univer- • Mars Reconnaissance Orbiter images of the Martian sity of Alabama in Huntsville. One of my main goals for surface (Chapter 11) those courses, and one of my main goals in this book, is • Trans-Neptunian Objects and the history of the solar to provide my students with a broad enough, deep enough system (Chapter 13) background in astronomy that they will be able to follow • Voyagers’ encounter with the termination shock of the current developments years after they fi nish my course. solar wind (Chapter 17) This book is current with recent developments such as the • Bright gamma ray burst of March 2008 (Chapter 20) cosmological discoveries of the WMAP satellite and the re- • VLBI determination of the size and rotation of the sults from the Mars rovers. But I want my students to con- Milky Way (Chapter 22) tinue to learn about astronomy long after these discoveries • Future collision between the Milky Way and M31 have been succeeded by newer, even more exciting, ones. (Chapter 25) I hope that years from now my students, and the readers • The Corot and Kepler missions to detect transits by of this book, will be able to read and watch stories about planets orbiting other stars (Chapter 27) astronomy with confi dence that they know what is going on and why the story is important. I can guarantee that future astronomical discoveries will occur at least as often Updated and Revised Topics as they do today, and I want my students to be prepared to • Diffraction (Chapter 6) enjoy future discoveries. • Large telescopes of the future (Chapter 6) I hope that all the explanations and descriptions in the • Information on future eclipses (Chapter 9) book will not obscure the awe and sense of wonder that • The loss of Venus’s water (Chapter 10) all astronomers feel when they pause in their work and • Discoveries by the Spirit and Opportunity rovers on think about the beauty of the universe. People have felt Mars (Chapter 11) that awe since prehistory and our wonderment has in- • The climate history of Mars (Chapter 11) creased as we understand more about the order and un- • Three newly defined dwarf planets (Chapter 13) derlying structure of the universe. If this book helps its • Icy plumes from Enceladus (Chapter 14) readers to value both the sheer beauty of planets, stars, and • P ossible future collisions of Apollo asteroids with Earth galaxies and the equally beautiful principles that organize (Chapter 15) the universe, it will be a success. • Brown dwarfs (Chapter 16) vi Preface vii • Massive black holes at the centers of galaxies (Chapter 23) Running Summaries • Planets orbiting other stars (Chapter 27) Important concepts and facts are summarized in the body of the chapter immediately after the concept is introduced. New and Updated Images Including images from Hubble, Spitzer, Spirit, Opportunity, Cassini, Huygens, Mars Global Surveyor, and Phoenix. Pedagogical Features The epicyclic model perfected by Ptolemy used Electronic Media Integration To help better grasp combinations of circular motions to reproduce key concepts, this interactive icon the motions of the planets. The model could pre- has been placed near fi gures and dict the positions of celestial objects with such selections where students can gain accuracy that it was used for nearly 1500 years. additional understanding through the interactives on the Astronomy Online Learning Center. To help better understand key con- AANNIIMMAATTIIOONN cepts, this animation icon has been Planetary Data Boxes placed near figures and sections These boxes include summaries of planetary data making where s tudents can explore additional information on the this information easy to access. Astronomy Online Learning Center. Chapter Introduction Every chapter begins with an introduction designed to give the historical and scientifi c setting Table 12.1 for the chapter material. The overview previews the chapter’s contents and what you can expect to learn from reading the chapter. After reading the introduction, browse through the Jupiter chapter, paying particular attention to the topic headings and illustrations so that you get a feel for the kinds of ideas in- Orbital distance 5.2 AU cluded within the chapter. Also included in the chapter intro- Orbital period 11.9 years duction are questions to explore while reading the text. Mass 318 M 1.90 1027 kg Earth Diameter 11.2 D 142,980 km Earth Worked Examples Boxes This book, like my course, Density (relative to water) 1.33 presumes that many of its readers are not science majors and Escape velocity 60 km/s may not have had a college-level science or mathematics Surface gravity 2.54 g Global temperature 125 K course. The book provides a complete d escription of current Main atmospheric gases H, He astronomical knowledge, neither at an extremely technical Rotation period 9.9 hours level nor at a level that fails to communicate the quantitative Axial tilt 3 nature of physical science. I have used equations where they Known satellites 63 are relevant, but follow the equations with boxes containing Distinguishing features Most massive planet, one or more worked exa mples. The e xamples in the boxes conspicuous cloud show how and when to use each equation and tell why the features equation is important. Historical Emphasis Throughout the book I have emphasized the historical development of astronomy to show that astronomy, like other sciences, ad- vances through the efforts of many scientists Equations Sidereal and Synodic Periods and to show how our present ideas developed. 4.41. 2and Ethqeu astyinoonds ic4 .p1e arinodd 4o.f2 ac apnla nbeet ufsroemd tiots csaildceurlaetael E0.q2u5a ytieoanr s4.. 2F oisr P 0.25 years and PEarth 1 year, In the main body of the text there are many period or vice versa. Suppose there were a supe- 1 1 1 comparisons of what was once known about a rSio r p1la.5n eyte awrsit ha nad s PyEnaortdhi c p 1e ryioeda r,o Ef q1u.5a tyioena r4s..1 F iosr (0.25 yr) (1 yr) S particular phenomenon to what we now know 1 1 1 (3 2) 1 Rearranging this equation to solve for 1兾S gives about it. These historical comparisons are used P (1 yr) (1.5 yr) (3 yr) (3 yr) 1 1 1 4 1 to illustrate the cycle of observation, hypoth- Thus, P, the sidereal period of the planet, is S (0.25 yr) (1 yr) (1 yr) (1 yr) 3 years. This is the hypothetical planet described 3 esis, and further observation, which is the es- in Figure 4.6. As a second example, suppose there (1 yr) were an inferior planet with a sidereal period of for which S 1兾3 year. sence of the scientifi c method of discovery. viii Preface End of Chapter Material Figure-Based Questions require the reader to extract the Chapter Summary highlights the key topics of the answer from a particular graph or figure in the chapter. chapter. Group Activities encourage interaction between stu- Key Terms listed here are defined in the text and in the dents as they work in groups to discuss different view- end-of-book glossary. points on chapter-related issues or to complete small Conceptual Questions require qualitative verbal answers. group projects. Problems, involving numerical calculations, test the reader’s mastery of the equations. 492 Chapter 20 White Dwarfs, Neutron Stars, and Black Holes Chapter Summary 491 Key Terms For More Information 493 black hole 489 gravitational Schwarzschild supernova remnant 478 • d Ae gwehnietrea tde waerlef citsr oan sp. laMneat-sssiizveed wsthairt Ces uphdpwaoarrptfesdt eabrrye Sumflaorrmgme eamd arngyenuettrico nfi esltda.r (2sp0i.n2s) very rapidly and has a Ceggvaelhieommandnmtei tdsh airc o ar rs4aie y7zk4 o1hb8nau6 rr st4s8 9 477 mnnpueeraeuulgsdttanrrsroohe nnti afi tr4zs at8 a t1ir44o 88n 83 4 74474 sssspppuraaapacccdeeeerilttuniiiksmmo evee at 4 rd i8 ip4a49 g87 r43a4m86 485 sttwiyyemhpnmiecet heilIis rkIsdo ieoswt urntaorp rinepf r 4snt 7oa48rv 8a 6 4 74074 3323.. gapSW ruuawhplvsaypeitt ocydrsh aeoi ts eeat so an r eEnacmshiontenarscoietnknex siian shutc’eseto rn n fttahps lteuflaoiolnnsrregcty e tar?ooas fwt eshar. ereSdl ah ftaaei lv blisnlt ayocc tlkoeim ssh etporh llyetao tu thshtheeadert 3356.. safDTahrhleeilf se tmct sors.oip wbWveaeicr nhtdwrgy ah a rda oaobtpf el wiaswdcnelhk’ ytw i thtaeohow uildsael wdy.im afsrrepfoelsmy i uft shuwuasae?t l lmwy aostshctho wewdh ilaatenr g doew brjaeerdcf-st smaller than low-mass white dwarfs. The Chan- • P ulsars are rotating neutron stars that emit beams of black hole. (Obviously, this astronaut is tough.) Why, 37. What are the only things we can tell about the drasekhar limit, the greatest mass that a white dwarf radiation. The rotation of the neutron star causes the if clocks run more slowly in strongly curved regions nature of the material within a black hole? • cA a nw hhaitvee ,d iws aarbfo kuet e1p.s4 aM c䉺o.n s(tSaenctt iosinz e2 0as. 1i)t evolves. bpeualsmess toof srwadeeiapt ipoans ta tsh eo fEteanrt ha,s coanuesi nthgo uuss taon do btsiemrvees Conceptual Questions oraft es pdaoceestnim’t ec,h danogese ?the astronaut find that her pulse 38. tWheh aStu wno aunldd htahpep leenn gtoth t hoef dtihstea nyceea ro fif t hthe eE aSrutnh fwroemre It radiates away its heat and grows cooler and dimmer per second. (20.2) 1. Describe the main difference between the mass-radius 16. Why are many supernova remnants bright in the 34. What effect does the curvature of spacetime have on i nstantly replaced by a 1 M䉺 black hole? simultaneously. After billions of years, a white dwarf • T he beamed radio emission from pulsars is probably relationship for main sequence stars and the mass- radio part of the spectrum? the frequency of radiation passing through it? becomes so dim it is difficult to detect. (20.1) produced by energetic electrons in regions near the radius relationship for white dwarf stars. 17. Why does the expansion of a supernova remnant slow • Wtlaoytheicirt se ga isda wncota orbfl rwsatniancrdsh s e.s vAtoa lrsvste a trfh rlaioktm eh tathhveee S cluoonsr tew st ihollef p irar soyodmuutpceer- mtehnaeeg rrngoyet taaitcsi otpnimo laeexs i,ps awossfhe iasc hapn uadlrs,ea ar.ft tiPeprup lepsdae rrshw aliopthsse 1 rr0eos tpmaeticilotli notanol 2. 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(20.2) 6. What is the relationship between the central stars of or pulsating neutron stars? through the star. After a few hours, the shock wave • S pacetime is the combination of three space coordi- planetary nebulae and white dwarf stars? 22. 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We cannot see that 10. Why does the process of neutronization reduce the 27. Why is a stationary body represented by a vertical originate in distant galaxies. Most gamma ray bursts space time is curved, so we have invented the force ability of the degenerate electrons in the core of a line rather than a point in a spacetime diagram? amrea spsirvoeb satbalrys . p(r2o0d.2u)ced by the collapses of cores of omf ogvrianvgi tb y otdoi eas.c c(o2u0n.3t) for the motion of light and 11. m Wahsasitv aer eA GthBe psrtaorc etsos essu tphpaotr rte tvheers ew tehigeh itn ofafl lt hoef mstaart?- 28. dWiahgyr acman?’t a body move horizontally in a spacetime Group Activity • srTupe 1 eyn0prhmnoe, e0crtdn hgh0ubayer0cnlo a esttes t urtlovoea r irnc oso1ti flrbu 0uorgln0amenadd, s0siuii na0nseito0ignjinueo cgisnyntt eh,ert asdaeeurwd r spsf,ihst oreueiotr clphmntlhaeeeo rrl ev nmassgao uc aavsopsukrap eee paremsenrns er.odn namvA a oahnnfsv teuataer.anp e rtst emsH wa rnbnieeitmoogae hnpvutioas-ttt • caenobA vo flo a enrbttcen ehlke atuoev ct fhhekre naooo v h lrneseliotni z agliotsrehn t n hawt f,.sroo .hoTt rrlehimTahznrroheos tn meuhSa ,gs ceab ihh ssacls aw oew3rcrsae khe.rks zui(imchss2lhc to0 t h tolo.niei3omfl od ) itmte shhrs aae ibtnds ohscigiouuev lscnelm,aa d tntpoaeh ssd eeebs m eroobcaeffyod r ttmgihhiueteeess, 111324... 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(20.2) • A ll that we can ever learn about a black hole gamma ray bursts and supernovae? form the sides of the triangle. You then used a pro- • Neutron stars, about 10 km in radius, are supported is its mass, angular momentum, and electrical 15. Only a small percentage of the energy of a type II tractor and found that the sum of the angles of the For More Information bmgtirymeo adratetee egsdmte natmesors aaivsbtseee ntnbheeeauuttwt trraeooe nnnns .e s1uLt.ta5irrko se an naw rdseht ai2ttre.h 7 ecd aMwnsma 䉺rhaf.a l lsvAetesa tr.nsi s,eT wtehhlsyee- chi snuhofrawlrruoegeuvenen. crdW,e i nbet gyhc saa.l not( o2dkt0ehi.tn3eeyg)c t fhtohare v teph reeo snset nroctehn egoi frg brialmavcimkta ethidooilnaetase,l soouff pmtehraent toeenvrae briglsay s ctraeerdlre iaeosdue tdaw wianar dyt .h bWey ehrxaapdtl iohastaiipoonpne? nans dto t hthe es hreesltl t Emraioarrntehg ltiehs awcnua rs1v 81e0d8⬚0, ?⬚s.o Ywohuy k dniodwn’ tt hyaotu trh ter isaunrgflaec ec oonf ttahine Vfeoxisre irct chtihaseep stte,e rax nqt duw izoezbtehssei,tr e ins attuet rdwaycw ttiowvoe.ml sle.hahren.icnogm /fix End-of-Text Material At the back of the text you will fi nd appendices that will give you additional background details, charts, and extensive tables. There is also a glossary of all key terms, an index organized alphabetically by subject matter, and constellation maps for reference. Supplements McGraw-Hill offers various tools and technology products to support Astronomy: Journey to the Cosmic Frontier, Sixth Edition. Instructors can obtain teaching aids by calling the Customer Service Department at 800-338-3987 or contacting your local McGraw-Hill sales representative. Interactives McGraw-Hill is proud to bring you an assortment of 23 outstanding Interactives like no other. Each Interactive is Preface ix programmed in Flash for a stronger visual appeal. These • T ext-specific features: Includes Multiple Choice Interactives offer a fresh and dynamic method to teach Quizzes, C onceptual Questions, Problems, Figure- the astronomy basics. 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This ever-growing resource gives instructors the power to utilize assets specifi c www.mhhe.com/fi x McGraw-Hill offers a wealth to an adopted textbook as well as content from all other of online features and study aids that greatly enhance the books in the library. astronomy teaching and learning experience. The design of the Fix website makes it easy for students to take full advantage of the following tools: Nothing could be easier! Accessed from the instruc- • I nteractive student technology: Includes 23 outstanding tor side of your textbook’s website, Presentation Center’s Astronomy Interactives, Animations, and Constellation dynamic search engine allows you to explore by discipline, Quizzes. course, textbook chapter, asset type, or keyword. Simply x Preface browse, select, and download the fi les you need to build Electronic Book If you or your students are ready engaging course materials. 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To review comp copies or to purchase an eBook, go to Instructor’s Manual The Instructor’s Manual www.CourseSmart.com is found on the Astronomy website (www.mhhe.com/fi x) and on the Instructor’s Testing and Resource CD, and can Acknowledgments be accessed only by instructors. I am grateful to many people who helped in the devel- Classroom Performance System and Questions opment and production of this book. Perhaps the most The Classroom Performance System (CPS) brings inter- i mportant contributors to the book are the more than ten activity into the class room/lecture hall. CPS is a wireless thousand University of Iowa and University of Alabama response system that gives an instructor immediate feed- in Huntsville students who took my beginning astronomy back from every student in the class. Each CPS unit comes classes. They taught me how to teach introductory as- with up to 512 individual re sponse pads and an appropri- tronomy and showed me the ingredients a good textbook ate number of corre sponding receiver units. The wireless must have. I owe a large debt to my fellow astronomers: re sponse pads are essentially remotes that are easy to use Andrea Cox, Ken Gayley, Larry Molnar, Bob Mutel, and engage students. The CPS system allows in struc tors John Neff, Stan Shawhan, Steve Spangler, and James Van to create their own questions or use the McGraw/Hill- Allen. Their help ranged from years’ worth of lunchtime provided astronomy questions. discussions about astronomy teaching to expert advice on