Astronomy Today 9th Edition

Book Preface

Astronomy is a science that thrives on new discoveries. Fueled by new technologies and novel theoretical insights, the study of the cosmos continues to change our understanding of the universe. We are pleased to have the opportunity to pre-sent in this book a representative sample of the known facts, evolving ideas, and frontier discoveries in astronomy today.

Astronomy Today has been written for students who have taken no previous college science courses and who will likely not major in physics or astronomy. It is intended for use in a one- or two-semester, nontechnical astronomy course. We present a broad view of astronomy, straightforwardly descriptive and without complex mathematics. The absence of sophisticated mathematics, however, in no way prevents discussion of important concepts. Rather, we rely on quali-tative reasoning as well as analogies with objects and phe-nomena familiar to the student to explain the complexities of the subject without oversimplification. We have tried to communicate the excitement we feel about astronomy and to awaken students to the marvelous universe around us.

We are very gratified that the first eight editions of this text have been so well received by many in the astronomy education community. In using those earlier texts, many teachers and students have given us helpful feedback and constructive criticisms. From these, we have learned to communicate better both the fundamentals and the excite-ment of astronomy. Many improvements inspired by these comments have been incorporated into this new edition.

Focus of the Ninth Edition

From the first edition, we have tried to meet the challenge of writing a book that is both accurate and approachable. To the student, astronomy sometimes seems like a long list of unfamiliar terms to be memorized and repeated. Many new terms and concepts are introduced in this course, but we hope students will also learn and remember how sci-ence is done, how the universe works, and how things are connected. In the ninth edition, we have taken particular care to show how astronomers know what they know, and to highlight both the scientific principles underlying their work and the process used in discovery.

New and Revised Material

Astronomy is a rapidly evolving field and, in the three years since the publication of the eighth edition of Astronomy Today, has seen many new discoveries covering the entire spectrum of astronomical research. Almost every chapter in the ninth edition has been substantially updated with new information.

Several chapters have also seen significant reorganization in order to streamline the overall presentation, strengthen our focus on the process of science, and reflect new understand-ing and emphases in contemporary astronomy.
In addition to updates throughout the text on the numbers and properties of the many astronomical objects, the many substantive changes include:

• New discussion in Chapter 5 of next-generation tel-escopes and high-resolution astronomy.
• Updated information and imagery in Discovery 5-1 on the ALMA array.
• New discussion in Chapter 8 of ice on the Moon.
• Additional coverage in Chapter 8 of Mercury’s surface and interior based on Messenger data.
• New discussion in Chapter 10 of the depletion of the Martian atmosphere.
• Expanded coverage in Chapter 10 of the Curiosity rover on Mars and its findings so far.
• Update in Chapter 11 on the changing appearance of Jupiter’s Great Red Spot.
• New material in Chapter 11 on the 2016 Juno mission.
• Updated discussion in Chapter 11 of the internal structure of Ganymede.
• New discussion in Chapter 12 of storms on Saturn.
• Expanded coverage in Chapter 12 of lakes and other features on the surface of Saturn’s moon Titan.
• Additional material in Chapter 12 on Saturn’s moon Enceladus.
• Update in Chapter 13 on the return of Neptune’s Dark Spot.
• New coverage in Chapter 14 of the Dawn mission to Ceres.
• Extensive discussion in Chapter 14 of the Rosetta mission to comet 67 P/Churyumov–Gerasimenko.
• Completely revised presentation of Pluto in Chapter 14 based on data from the New Horizons mission.
• Updated and rewritten presentation in Chapter 15 of exoplanet searches and properties.
• New material in Chapter 15 on direct imaging as an exoplanet detection technique.
• Expanded discussion in Chapter 15 of exoplanet composition.
• Presentation in new Discovery 15-1 of gravitational microlensing as an important exoplanet detection technique.
• Updated discussion in Chapter 15 of habitable zones and planetary systems in star clusters.

• Additional material in Discovery 16-1 on the Solar Dynamics Observatory.
• Substantially improved discussion and imagery in Chapter 16 of the sunspot cycle.
• New coverage in Chapter 17 on the GAIA astrometric mission.
• Additional material in Discovery 19-1 on brown dwarfs, clarifying the distinction between brown dwarfs and planets.
• Improved text and imagery in Chapter 19 on the observational evidence for various stages of star formation: ALMA imagery of protostellar collapse; HST observations of protoplanetary disks.
• Improved simulations of star cluster formation in Chapter 19.
• Expanded discussion in Discovery 20-2 of mass loss from giant stars.
• Emphasis in Chapter 22 of the connection between hypernovae and black holes.

• Expanded treatment in Discovery 22-1 of relativity and time dilation.
• Rewritten discussion of gravitational radiation in Discovery 22-1, including extensive coverage of the 2015 LIGO detections.
• Reconsideration in Chapter 22 of the existence of black holes, in the light of the new LIGO findings.
• New coverage in Chapter 23 of the “X” in the Milky Way bulge and its implication for our Galaxy’s history.
• Expanded material in Chapter 23 on the “S stars” in the Galactic center and energetic outflows from the Galactic center into the halo.
• Updated discussion of extremophilic life in Chapter 28.
• Consistent distance scales in all figures, helping students gain an understanding of the vastness of the universe.
• Numerous replacement images for currency and clarity, and updated art throughout the text.

BRIEF CONTENTS

PART I: Astronomy and the Universe 2
1 Charting the Heavens: The Foundations of Astronomy 5
2 The Copernican Revolution: The Birth of Modern Science 33
3 Radiation: Information from the Cosmos 59
4 Spectroscopy: The Inner Workings of Atoms 79
5 Telescopes: The Tools of Astronomy 99
PART II: Our Planetary System 132
6 The Solar System: Comparative Planetology and Formation Models 134
7 Earth: Our Home in Space 160
8 The Moon and Mercury: Scorched and Battered Worlds 187
9 Venus: Earth’s Sister Planet 214
10 Mars: A Near Miss for Life? 233
11 Jupiter: Giant of the Solar System 260
12 Saturn: Spectacular Rings and Mysterious Moons 286
13 Uranus and Neptune: The Outer Worlds of the Solar System 314
14 Solar System Debris: Keys to Our Origin 333
15 Exoplanets: Planetary Systems Beyond Our Own 363
PART III: Stars and Stellar Evolution 384
16 The Sun: Our Parent Star 386
17 The Stars: Giants, Dwarfs, and the Main Sequence 417
18 The Interstellar Medium: Gas and Dust Among the Stars 445
19 Star Formation: A Traumatic Birth 465
20 Stellar Evolution: The Life and Death of a Star 490
21 Stellar Explosions: Novae, Supernovae, and the Formation of the Elements 516
22 Neutron Stars and Black Holes: Strange States of Matter 537
PART IV: Galaxies and Cosmology 570
23 The Milky Way Galaxy: A Spiral in Space 572
24 Galaxies: Building Blocks of the Universe 601
25 Galaxies and Dark Matter: The Large-Scale Structure of the Cosmos 632
26 Cosmology: The Big Bang and the Fate of the Universe 659
27 The Early Universe: Toward the Beginning of Time 681
28 Life in the Universe: Are We Alone? 70