ASTRONOMY ASTRONOMY A Self-Teaching Guide Seventh Edition Dinah L Moché, Ph.D John Wiley & Sons, Inc This book is printed on acid-free paper. Copyright â 1978, 1981, 1987, 1993, 2000, 2004, 2009 by John Wiley & Sons, Inc All rights reserved Published by John Wiley & Sons, Inc., Hoboken, New Jersey Published simultaneously in Canada No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except as permitted under Sections 107 or 108 of the 1976 United States Copyright Act, without either the prior written permission of the Publisher, or authorization through payment of the appropriate per-copy fee to the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, (978) 750-8400, fax (978) 646-8600, or on the web at www.copyright.com Requests to the Publisher for permission should be addressed to the Permissions Department, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030, (201) 748-6011, fax (201) 748-6008 Limit of Liability/Disclaimer of Warranty: While the publisher and the author have used their best efforts in preparing this book, they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose No warranty may be created or extended by sales representatives or written sales materials The advice and strategies contained herein may not be suitable for your situation You should consult with a professional where appropriate Neither the publisher nor the author shall be liable for any loss of profit or any other commercial damages, including but not limited to special, incidental, consequential, or other damages For general information about our products and services, please contact our Customer Care Department within the United States at (800) 762-2974, outside the United States at (317) 572-3993 or fax (317) 572-4002 Wiley also publishes its books in a variety of electronic formats Some content that appears in print may not be available in electronic books For more information about Wiley products, visit our web site at www.wiley.com Library of Congress Cataloging-in-Publication Data Moché, Dinah L., date Astronomy : a self-teaching guide / Dinah L Moché—7th ed p cm — (Wiley self-teaching guides ; 190) Includes bibliographical references and index ISBN 978-0-470-23083-1 (paper) Astronomy I Title QB45.2.M63 2009 520—dc22 2009025983 Printed in the United States of America 10 CREDITS We thank the American Astronomical Society for providing dozens of press releases, fact sheets, and celestial images This service enables us to keep this text accurate and up to date Figures are courtesy of the following organizations and individuals: David Aguilar/Harvard-Smithsonian Center for Astrophysics: 7.8 California Association for Research in Astronomy (adapted from): 2.15 C.S.I.R.O.: 2.17, 6.19c ESA/NASA/SOHO: 4.1, 4.8 ESO: 6.3, 6.16c Ann Feild/Space Science Telescope Institute: 6.23 Gemini Observatory/Neelon Crawford-Polar Fine Arts: 2.6 Hale Observatories: 6.4, 9.28, 11.5, 11.7 The Hubble Heritage Team (AURA/STScI/NASA: 6.21 Hubble Space Telescope WFPC Team, NASA, STScI: 6.16a Dr Thomas Jarrett: 6.17 JAXA: 4.9 Lowell Observatory: 9.22 Dinah L Moché/George Tremberger Jr.: I.2, I.3, 1.12, 2.4, 3.8, 3.9, 3.16, 3.17, 3.18, 3.20, 4.6, 5.3, 5.10 ([selected] data from Barbara J Anthony-Twarog), 6.6, 6.7, 6.8, 6.12, 6.24a, 6.24b, 6.25, 7.1, 7.2, 7.4, 8.1 ([selected] from NASA), 8.2, 8.4, 8.11, 8.12, 9.12, 9.14, 9.15, 10.8 NASA: I.1, 5.1a, 5.14, 8.14 (adapted), 8.16, 9.2, 9.6, 9.8, 9.9, 9.10, 9.18, 9.19, 9.21, 9.23, 9.26, 9.27, 10.1, 10.5, 10.6, 10.7, 11.1, 11.4, 12.3, 12.4, 12.5 NASA, Reta Beebe, and Amy Simon (New Mexico State University): 9.20 NASA/CXC/ASU/J Hester, et al.: 5.12b NASA/CXC/CfA/R Kraft, et al.: 6.19a NASA/CXC/MIT/F K Baganoff, et al.: 6.11 NASA and ESA: 6.16d NASA/ESA/ASU/J Hester & A Loll: 5.12a NASA and STScI: 6.16f NASA, ESA, S Beckwith (STScI) and the HUDF Team: I.4 NASA, ESA, R Gendler, T Lauer (NOAO/AURA/NSF) and A Feild (STScI): 6.14 NASA, ESA, and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration: 6.16b, 6.16e NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and A Evans (University of Virginia, Charlottesville/NRAO/Stony Brook University): 6.20 NASA and the Hubble Heritage Team (STScI/AURA): 5.9, 6.2 NASA, ESA and T Lauer (NOAO/AURA/NSF): 6.9 NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington: 9.1a, 9.1b NASA/JPL-Caltech: 6.10, 9.17 NASA/JPL-Caltech/M Meixner (STScI) & the SAGE Legacy Team: 6.13 NASA/JPL-Caltech/T Pyle (SSC): 12.2 NASA/JPL-Caltech/Univ Minn./R Gehrz : 5.12c NASA/JPL/Space Science Institute: 9.24 NASA/JPL/STScI: 9.25 NASA, Steve Lee (University of Colorado), Jim Bell (Cornell University), Mike Wolff (Space Science Institute): 9.16 NASA/WMAP Science Team: 7.9 National Optical Astronomy Observatories: 1.3, 5.11, 6.1, 6.5, 6.22a National Radio Astronomy Observatory/AUI, J O Burns, E J Schrier, and E D Feigelson: 6.18 v vi ★ ASTRONOMY Image courtesy of NRAO/AUI and Earth image courtesy of the SeaWiFS Project NASA/GSFC and ORBIMAGE: 2.18 J William Schopf, Elso S Barghoorn, Morton D Masser, and Robert O Gordon: 12.1 Dr Martin Schwartzchild, Princeton University: 4.10 Seth Shostak: 12.7 Aurore Simonnet, Sonoma State University, NASA E/PO: 2.19 SOHO (ESA & NASA): 4.7a, 4.12, 4.13 SOHO (ESA & NASA); assembled by Steele Hill (NASA GSFC): 4.11, 4.12, 4.13 SOHO/MDI magnetic map, white light, TRACE 1700A continuum, TRACE Lyman alpha, TRACE 171Å, TRACE 195Å, TRACE 284Å, YOHKOH/SXT X-ray image; composite prepared by Joe Covington (Lockheed-Martin Missiles and Space, Palo Alto): 4.7b (clockwise from top) STScI and NASA: 2.12 Tass/Sovfoto: 9.7 United States Air Force: 11.10 Courtesy John Walker: 4.5 Ryan Wyatt (adapted from): 8.3 Photo Insert Page top: NASA/Lockheed Martin [images from the NASA Transition Region and Coronal Explorer (TRACE), the Extreme ultraviolet Imaging Telescope (EIT), the Large Angle and Spectrometric coronagraph (LASCO), and the Michelson Doppler Imager (MDI) telescopes on the ESA/NASA Solar and Heliospheric Observatory (SOHO)]; page bottom: Courtesy NASA/JPL-Caltech; page top: X-ray: NASA/CXC/CfA/R.Kraft et al; Radio: NSF/VLA/Univ.Hertfordshire/M.Hardcastle; Optical: ESO/VLT/ISAAC/M Rejkuba, et al; page bottom: NASA, ESA, and The Hubble Heritage Team (STScI/AURA); page top left and right: NASA, ESA, and The Hubble Heritage Team (STScI/AURA); page bottom: NASA/WMAP Science Team; page top: X-ray: NASA/CXC/Wesleyan Univ./R Kilgard, et al; UV: NASA/JPL-Caltech; Optical: NASA/ESA/S Beckwith & Hubble Heritage Team (STScI/AURA); IR: NASA/JPL-Caltech/ Univ of AZ/R Kennicutt; page bottom: X-ray: NASA/UMass/Q D Wang, et al.; Optical: NASA/STScI/AURA/Hubble Heritage; Infrared: NASA/JPL-Caltech/Univ AZ/R Kennicutt/SINGS Team Tables and illustrations are adapted, redrawn, or used by permission of the following authors and publishers: Table 1.1: Robert Garrison and Toomas Karmo, Observer’s Handbook 2008, with permission of the Royal Astronomical Society of Canada Table 2.1: Astronomy: Fundamentals and Frontiers, 3rd edition, by Robert Jastrow and Malcolm H Thompson Copyright © 1972, 1974, 1977 by Robert Jastrow (John Wiley & Sons, New York) Table 3.1 (adapted); 11.2 (selected): Allen’s Astrophysical Quantities, 4th edition Copyright © 1999 by A N Cox, ed (Springer-Verlag, New York) Table 6.2 (adapted): Realm of the Universe, by George O Abell Copyright © 1964, 1969, 1973, 1980, by Holt, Rinehart and Winston, Inc Copyright © 1976 by George O Abell Used by permission of Holt, Rinehart and Winston, Inc Tables 8.2 and 8.3: (selected) National Aeronautics and Space Administration public information Updates by JPL’s Solar System Dynamics Group, URL: http://ssd jpl.nasa.gov/sat_elem.html Tables 10.2 and 10.3: with permission from Solar Eclipses: 1996–2020 and Lunar Eclipses: 1996–2020, by Fred Espenak, NASA/Goddard Space Flight Center Tables 8.3 and 11.1: (selected) Brian G Marsden, Smithsonian Astrophysical Observatory Appendix 5: Alan Batten, Observer’s Handbook 2009, with permission of the Royal Astronomical Society of Canada TO THE READER Astronomy is a user-friendly guide for beginners Chapters make it easy for you to quickly learn the main topics of a college level course Sections clarify basic principles and contemporary advances The Index enables you to look up concepts, definitions, facts and famous astronomers, fast You can use the book alone or with a conventional textbook, Internetbased or distance-learning course, computer software, telescope manual, or as a handy reference PARTICULARLY USEFUL FEATURES • • • • • • • • Web site addresses throughout for the best astronomy online Mathematics is not required Line art makes technical ideas obvious Star and Moon maps for fun stargazing Up-to-date, accurate star, constellation, and astronomical data Popular sky targets for hobby telescopes Tips for hands-on, active learning Objectives, reviews, and self-tests to monitor your progress WHAT’S NEW IN THE SEVENTH EDITION? While keeping its successful self-teaching format, this seventh edition incorporates Web site addresses for spectacular color images The entire book was revised to include revolutionary discoveries and the best suggestions from many readers and educators who profitably used prior editions Frontier twenty-first-century research into black holes, active galaxies and quasars, searches for life in space, origin and structure of our universe, and the newest ground and space telescopes are described vii viii ★ ASTRONOMY Web sites with daily astro-news and space scenes never before viewed by humans are specified Labeled drawings of the Keck Telescope, Fermi Gamma Ray Observatory, and Hubble Space Telescope data path clarify space technology New art illustrates fundamental concepts, such as the electromagnetic spectrum, phases of the Moon, planet orbits, and H-R diagrams STUDY AIDS A list of objectives for each chapter tells you instantly what information is contained there The first time a new term is introduced, it appears in bold type and is defined Topics in each chapter are presented in short, numbered sections Each section contains new information and usually asks you to answer a question or asks you to suggest an explanation, analyze, or summarize as you go along You will always see the answer to the question right after you have answered it If your answer agrees with the book’s, you understand the material and are ready to proceed to the next section If it does not, you should review some previous sections to make sure you understand the material before you proceed A self-test at the end of each chapter lets you find out fast how well you understand the material in the chapter You may test yourself right after completing a chapter, or you might take a break and then take the self-test as a review before beginning a new chapter Compare your answers with the book’s If your answers not agree with the printed ones, review the appropriate sections (listed next to each answer) USEFUL RESOURCES AND WEB SITES Sources of excellent print and online astronomy materials, activities, and references are included in the Useful Resources and Web Sites section Here you will also find a list of other books for stargazers of all ages by the author, Dinah L Moché, Ph.D The author and publisher have tried to make this book accurate, up-todate, enjoyable, and useful for you It has been read by astronomers and many students, hobbyists, and educators who have contributed helpful suggestions during the preparation of the final manuscript If, after completing the book, you have suggestions to improve it for future readers or for an author’s visit, please let the author know: Dinah L Moché, Ph.D., c/o Professional & Trade Group, John Wiley & Sons, Inc., 111 River Street, Hoboken, NJ 07030 ᭤www.spacelady.com᭣ Check this book’s Web site for exciting new discoveries, and updates and corrections in press for the next printing ᭤www.wiley.com/go/moche᭣ INDEX protostar, 123–124 Ptolemaic system, 208 Ptolemy, 208 Puck, 261 pulsars, 138–140 pulsating variable stars, 130 quasars, 166, 172–174 radial velocity, 75 radiant, 305–306 radiation pressure, 298 radiation spectrum, 39 radiation zone, 102 radio astronomy, 55 radio galaxies, 170 radiograph, 55 radio telescopes, 54, 55–57, 104, 157, 326 radio wavelengths, 172 radio waves, 35 rays, 277–278 red dwarf, 85, 87 red giants, 87, 128, 131 redshift, 76, 173 red supergiant, 128 reflecting telescope (reflectors), 40, 43–44, 50 refracting telescope (refractors), 40, 42 regolith, 279 regression, of the nodes, 288 regular clusters of galaxies, 167 Regulus, 11 resolving power, 45–46 retrograde, 233 retrograde loop, 206, 208 retrograde motion, 206 revolution, 203 ribonucleic acid (RNA), 316 richness, of galaxies, 167 Rigel, 14, 78, 128 right ascension (RA), 13, 15 Rosalind, 261 Rosetta, 295 rotation, 6, 26, 140 rotational broadening, 77 RR Lyrae, 130–131 Russell, Henry N., 84 Russian Luna missions, 282 Sagan, Carl, 319 Sagittarius A*, 158 satellite, 215 Saturn: asteroids orbiting, 224 compared with other planets, 218, 219 density, 257 history of, 204, 254 magnetosphere, 257 moons, 257–258 movement of, 206 rings, 254, 256 space travel to, 257 surface, 256 temperatures, 257 scarps, 231 Schiaparelli, G V., 244 Schmidt-Cassegrain telescope, 43, 50 Schwarzschild radius (Rs), 141 Scorpius, 128 seasons, 22–23 secondary mirror, 43 Second Index Catalog, 160–161 seconds of arc (Љ), 66 seeing, 48 segmented mirrors, 52 seismic waves, 116, 239 Seyfert, Carl K., 171 Seyfert galaxy, 171 Seyfert nucleus, 171 shield volcanoes, 237 Shklovsky, I S., 319 “shooting stars,” 304 short-period comet, 301 sidereal day, 25 sidereal month, 214 sidereal revolution period, 219 sidereal rotation period, 221 singularity, 142 Sirius, 11, 14, 82, 89, 348 Skylab, 115 Sloan Digital Sky Survey, 174 Small Magellanic Cloud (SMC), 161 Sojourner, 245–246 solar activity cycle, 110–111 Solar and Heliospheric Observatory (SOHO), 104 solar constant, 96 solar day, 25 solar eclipse, 284–286 solar nebula, 99, 282 solar nebular model, 203 Solar neutrino experiments, 116 solar system: contents of, 3, 202 first telescopic data, 209–210 history of, 208 motion and gravity, 212–213 ★ 359 360 ★ ASTRONOMY solar system (continued) origin of, 203 solar wind, 115 solstice, winter and summer, 23 south circumpolar constellations, south circumpolar stars, 19 Southern Cross, 19 South Pole, 17 spaceflight, 215–217 Space Interferometry Mission (SIM), 321 space shuttles, 322 space stations, 323 space velocity, 75 special relativity, 127 spectra: stellar, 71 types of, 68 spectral classes: characteristics, origin of, 75 defined, 72 spectral lines, 69–72, 116, 164 spectral line shape, 77 spectrograph, 53 spectroheliogram, 105 Spectroheliographs, 105 spectrophotometry, 221 spectroscope, 54 spectroscopic binary stars, 89 spectroscopy, 68 spherical aberration, 50 spicules, 107 spiral galaxies, 150, 159, 163, 165, 171 Spitzer Space Telescope (SST), 57 Sputnik 1, 215 standard candle, 164 starburst, 158 starburst galaxy, 171 star clusters, 150 Stardust, 295 stars: annual motion of, 20–21 brightness, 11 chemical composition, 71–72, 125 daily motion of, 17–20 distances to, 66–67 life cycle of, 122–131, 153–154 location on Earth, 12 luminosity, 78 magnetic fields, 111, 114–115 mass, 125, 131 motions, generally, 75–77 names, 10–11 origin of, 315–316 probes, 324–325 radiation laws, 38–39 revolution, 20 spectral classes, 72–73, 75 stellar spectra, 71 temperature, 74–75 starspots: cycles, 116 defined, 116 Steady State models, 182 Steady State theory, 189 Stefan-Boltzmann radiation law, 39, 87 stellar evolution: defined, 122 overview, 122–142 theory of, 122, 152 stellar spectra, 71 stellar wind, 133 Stickney, 250 stony-iron meteorites, 307 stony meteorites, 307 Stratospheric Observatory for Infrared Astronomy (SOFIA), 57 structure, of galaxies, 167 S-type asteroids, 221 Sun: altitude, 24 annual motion of, 21–22 asteroids and, 224 composition of, 71–72, 100, 127 diameter of, 87, 97 Earth and, 96–97, 237 eclipse of, 284–285 ecliptic, 21 history of, 204, 208 location of, 14 luminosity, 78, 96, 127 mass of, 87, 165 motion, 117 observations, 104–107 rotation, 103 size, 97 structure of, 100–102 surface of, 107–108 Sun’s angular diameter, 97 sunspots: cycle, 110 defined, 108 maximum, 110 minimum, 110 supercluster, 168 supergiants, 85 supergranules, 107 superior conjunction, 208 superior planet, 203 INDEX supernova: defined, 136 remnants, 136–138 Type Ia, 134, 165, 192 Type II, 136 Supernova 1987A, 137 Swift, Jonathan, 250 synchronous rotation, 273 synchrotron radiation, 170 synodic month, 206 synodic revolution period, 219 synodic rotation period, 221 syzgy, 214–215 targeted search for extraterrestrial life, 328 Tau Ceti, 326 Taurus, 138 telescopes, 31–59, 221 design and selection of, 50–53 enhancements, 53 function of, 39 optical, 40–41 size of, 41 See also specific types of telescopes Tereshkova, Valentina V., 323 terminator, 278 Terra Aphrodite, 236 terrestrial globe, 12 terrestrial planets, 218 Tertiary Era, 310 thermal radiation, 38 Thuban, 27, 83 Titan: generally, 257 life on, 319 Titania, 260, 261 Tombaugh, Clyde, 265 total eclipse, 284 tracks of evolution, 122 transit, 16, 233 Triangulum, 167 Triton, 263–264 Tucana, 161 Tully-Fisher relation, 164 21-centimeter radiation, 157 ultraviolet telescopes, 58, 105 Ulysses, 107 umbra, 109 unidentified flying objects (UFOs), 325 universal laws, 213 universe: age of, 196 expansion of, 182–183 matter and energy, 192–193 models of, 187–188, 208 radiation, 193 shape of, 196–197 size of, 196–197 Uranus: atmosphere, 259 compared with other planets, 218, 219 discovery of, 258–259 magnetosphere, 259 moons, 260–261 rings, 259 temperature, 259 Ursa Major, 10, 89, 342 Ursa Minor, 10 Van Allen belts, 242 Vega, 11, 14, 27, 72 Venera spacecraft, 234 Venus: atmosphere, 234 compared with other planets, 218 craters on, 236 cycle of phases, 232–233 greenhouse effect on, 235, 243 history of, 204, 209, 232 life on, 318 movement of, 206 observations, 232–233 phases, 209–210 surface of, 235 temperatures, 235 vernal equinox, 13, 23, 27 Very Large Array (VLA), 55–56 Very Large Telescope (VLT), 52 Very Long Baseline Array, 56 Very Long Baseline Interferometry (VBLI), 56 Vesta, 221 Viking spacecraft, 245, 318–319 Virgo, 8, 10, 342 Virgo cluster, 168 visible light, 33 visible spectrum, 33 visual binary stars, 88 voids, 168 volcanoes: on Earth, 316 on Mars, 247 on Moon, 276–277, 282 Vostok spacecraft, 322–323 ★ 361 362 ★ ASTRONOMY Voyager, 216–217, 250, 253, 254, 257, 259, 260–261, 262, 263, 324–325 walled plains, 277 wave, 32 wave equation, 37 wave frequency, 36 wavelength, 32–33, 38, 70, 76, 157–158 wave propagation, 37 Whipple, Fred, 296 white dwarfs, 85, 87, 134 Wien’s law of radiation, 38 Wilson, Robert, 193 WIMPs, 192 X-ray bursters, 140 X-rays, 35, 101, 117, 142, 168, 1581 X-ray telescopes, 58, 105 Yerkes Observatory, 41 Z, 173, 182 Zeeman effect, 77 zenith, 15, 17 zodiac: defined, 21, 27 signs, 21, 27 STAR AND MOON MAPS 363 Multi-wavelength images of the Sun from the TRACE and SOHO spacecraft Montage of the planets and smaller bodies in the solar system False color composite of galaxy Centaurus A from X-ray, optical, and radio data shows the effects of an active supermassive black hole Antennae Galaxies An interacting pair whose streamers of stars, about a hundred thousand light years long, were created when they collided Star-forming region NGC 3603, about 20,000 light-years away in the Carina spiral arm of our Galaxy Expanding halo of light in interstellar dust around red giant star V838 Monocerotis (V838 Mon), about 20,000 light-years away in the constellation Monoceros Detailed, all-sky picture of the infant universe from WMAP data reveals 13.7 billion-year-old temperature fluctuations (shown as color differences) Whirlpool Galaxy (M51) False color composite from multi-wavelength data has purple (X-ray) black holes and neutron stars in binary star systems, green (optical) and red (infrared) lanes of stars, gas, and dust and blue (ultraviolet) hot, young stars Edge-on view of the Sombrero galaxy (M104) False color shows blue (X-ray) hot gas, objects within, and quasars, and green (optical) and red (infrared) rim of dust around a central bulge of stars Science/Astronomy DISCOVER THE WONDERS OF THE NIGHT SKY WITH THIS BESTSELLING ASTRONOMY GUIDE From stars, planets, and galaxies to black holes, the Big Bang, and life in space, Astronomy has introduced hundreds of thousands of people worldwide to the secrets of the universe A unique, successful self-teaching format makes it easy for you to quickly grasp basic principles and keep up with contemporary discoveries You can use this user-friendly book alone or with a textbook, modules, Internet-based or distance-learning course, computer software, telescope manual, or as a handy reference Updated with the latest, most accurate information and more than 100 new graphics and photos, this Seventh Edition features: • Web site addresses throughout for the best color images and astronomy resources online • Technical ideas made simple without mathematics • A beautiful new full-color, glossy insert with spectacular astro-images • An interactive format with learning goals, reviews, self-tests, and answers for fast learning • Five beginners’ Star and Moon maps for fun stargazing Praise for previous editions of Astronomy : “One of the best ways by which one can be introduced to the wonders of astronomy.” —The Strolling Astronomer “Excellent provides stimulating reading and actively involves the reader in astronomy.” —The Reflector DINAH L MOCHÉ, PhD, is Professor of Physics and Astronomy at the City University of New York and an award-winning author and lecturer Her books have sold more than ten million copies in seven languages Cover Design: José Almaguer Cover Photographs: Top Photo, Space Planets/ © Mark Plumly/Dreamstime.com; Bottom Photo, M82 Starburst Galaxy © STScl/NASA/Corbis $19.95 USA/$23.95 CAN ... University): 9.20 NASA/CXC/ASU/J Hester, et al.: 5.12b NASA/CXC/CfA/R Kraft, et al.: 6.1 9a NASA/CXC/MIT/F K Baganoff, et al.: 6.11 NASA and ESA: 6.16d NASA/ESA/ASU/J Hester & A Loll: 5.1 2a NASA and STScI:... ESO/VLT/ISAAC/M Rejkuba, et al; page bottom: NASA, ESA, and The Hubble Heritage Team (STScI/AURA); page top left and right: NASA, ESA, and The Hubble Heritage Team (STScI/AURA); page bottom: NASA/WMAP... page bottom: X-ray: NASA/UMass/Q D Wang, et al.; Optical: NASA/STScI/AURA/Hubble Heritage; Infrared: NASA/JPL-Caltech/Univ AZ/R Kennicutt/SINGS Team Tables and illustrations are adapted, redrawn,