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Discovering Astronomy:

Stars, Galaxies, and Universes

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Discovering Astronomy: Stars, Galaxies, and Universes Course Outline

Chapter One: Beyond the Blue Horizon: A Grand Tour of the Universe

Chapter Synopsis: We begin where astronomy began — with people observing the sky. Astronomy is first and foremost an observational science; only after astronomers have made observations of phenomena does interpretation based on theory come into play. The first chapter is a grand tour of the universe. We begin with a brief look at the sorts of objects that inhabit it. In addition, we take a first look at the vast range of sizes and distances of the universe’s components.

Section 1.1 – What is Astronomy?

Section 1.2 – Our View of the Cosmos

Section 1.3 – The Solar System

Section 1.4 – Stars, Galaxies, and Beyond

Section 1.5 – Where does astronomy Go


Chapter Two: Science and Pseudoscience

Chapter Synopsis: In the first part of this chapter you will learn what science is, using astronomy as an example. In the second part, we further define science by showing what is not science. Finally, we examine various characteristics of what often pretends to be science but isn’t.

Section 2.1 – An Expedition to Earth

Section 2.2 – Astronomy as an Observational Science

Section 2.3 – Science as a Process

Section 2.4 – Is It Science or Pseudoscience?

Section 2.5 – Do New Ideas Displace the Old Ones?


Chapter Three: Astronomical Observations: Angles and Uncertainties

Chapter Synopsis: Beginning with this chapter, this book contains a variety of activities called Discoveries at the end of some chapters. Working with these Discoveries, you can become actively involved in learning astronomy and have the opportunity to make simple but meaningful measurements. These Discoveries also give a deeper understanding of both the subject matter and the methods of astronomy. A guiding philosophy of this book is to make active learning experiences available wherever possible. Discoveries are self-contained in the text and allow you the opportunity to do something with available data.

Section 3.1 – Angles and Angular Measurement

Section 3.2 – Angles on the Celestial Sphere

Section 3.3 – The Relationship between Physical and Angular Size

Section 3.4 – Measurement Uncertainty

Section 3.5 – Systematic Uncertainties in Astronomy: The Kapteyn Universe as an Example


Chapter Four: Basic Observations and Interpretations of the Sky

Chapter Synopsis: In this chapter, we look first at fundamental observations in this chapter. Then, in the next chapter, we build a model that best explains the observations while also making testable predictions.

Section 4.1 – Early Observations of the Sky

Section 4.2 – Early Greek Observations: The Round Earth

Section 4.3 – The Observed Motions of the Sky

Section 4.4 – The Motion of the Sun

Section 4.5 – The Reasons for the Seasons

Section 4.6 – The Location of Stars on the Celestial Sphere

Section 4.7 – The Motion and Phases of the Moon

Section 4.8 – The Motions of the Planets

Section 4.9 – How Stars Get Their Names

Section 4.10 – Measuring Star Brightness


Chapter Five: The Historical Quest to Model the Solar System

Chapter Synopsis: In this chapter we follow the way our knowledge of the layout of the Solar System developed from the time of the Greek Earth-centered view to the Sun-center view during the renaissance in Europe. We will be interested in how the ideas that developed in one era were a natural outgrowth of the state of astronomical observations and degree of sophistication of the times.

Section 5.1 – Greek Astronomy

Section 5.2 – Astronomy during the Middle Ages

Section 5.3 – The Heliocentric Hypothesis

Section 5.4 – Kepler’s Laws of Planetary Motion

Section 5.5 –  The Search for Underlying Laws

Section 5.6  – Evidence in Favor of the Heliocentric Hypothesis

Section 5.7  – Observational Evidence of the Earth’s Rotation


Chapter Six: The Nature of Light

Chapter Synopsis: What is light? To get a handle on that question we will examine three models that allow us to think about the nature of light — as a ray, a wave, or a particle. These three models allow us to describe and predict light’s behavior and to extract detailed information from light of all types.

Section 6.1 – Light as a Ray

Section 6.2 – Light as a Wave

Section 6.3 – Light as a Stream of Particles


Chapter Seven: Telescopes - Our Eyes of Discovery

Chapter Synopsis:  In this chapter, you will study how lenses and mirrors form images, and how combinations of lenses and mirrors form telescopes. In addition you will read about the auxiliary instruments that are attached to telescopes to detect the light. Finally, we discuss the places at which telescopes are located on Earth as well as NASA’s Great Observatories in space.

Section 7.1 – The Formation of Images

Section 7.2 – Telescopes

Section 7.3 – Comparing Reflecting and Refracting Telescopes

Section 7.4 – Reflecting Telescopes of Various Types

Section 7.5 –  The Telescopes of the Future

Section 7.6 – Detectors and Instruments

Section 7.7 – Radio Astronomy

Section 7.8 – Optical and Radio Observatory Sites

Section 7.9 – Beyond Optical and Radio Astronomy

Section 7.10 – NASA’s Great Observatories


Chapter Eight: Spectra - The Key to Understanding the Universe

Chapter Synopsis: In this chapter we investigate the three principal types of spectra and learn their significance. We will also examine the principles by which the chemical compositions of and physical conditions in stars can be measured. Finally, we apply these principles to analyzing various sources of radiation both in the laboratory and in the outside world.

Section 8.1 – Observations of Spectra

Section 8.2 – Understanding Spectra

Section 8.3 – Applications of Spectroscopy


Chapter Nine: Understanding Stellar Spectra

Chapter Synopsis: Classifications are like boxes into which similar objects are placed. Such classifications provide opportunities to see similarities and differences among objects. Astrophysicists classify galaxies (see Chapter 16) and stars according to their physical properties and appearance. As we shall see, stars can be classified on the basis of their spectrum (this chapter), their variation in light output (Chapter 13), and their membership in clusters of stars (Chapters 10 and 13). Because so much of what we know about the universe comes from an analysis of spectra, we now turn to looking at stellar spectra in some detail.

Section 9.1 – Classification of Stellar Spectra

Section 9.2 – The Cosmic Abundance of the Chemical Elements

Section 9.3 – The Doppler Effect

Section 9.4 – What We Can Learn from Spectral Lines


Chapter Ten: The Observed Properties of Normal Stars

Chapter Synopsis: Astronomers use a variety of techniques to find the fundamental properties of stars. We begin by learning how they use parallax to determine directly the distance to the nearest stars. Distance, while important, is an external property that is independent of the intrinsic properties of stars.

Section 10.1 – Distance Measurements

Section 10.2 – Binary Stars and Stellar Masses

Section 10.3 – Binary Stars and Other Stellar Properties

Section 10.4 – The Hertzsprung-Russell Diagram

Section 10.5 – Main-Sequence, Giant, Supergiant, and White Dwarf Stars

Section 10.6 – Explanation of the Main Sequence

Section 10.7 – Stellar Distances and the H-R Diagram


Chapter Eleven: Energy Source and Structure of the Sun and Stars

Chapter Synopsis: One of the most dramatic examples of the importance of basic research is the discovery of nuclear fission and nuclear fusion. Although few discoveries have had more practical implications for the survival of humanity, the basic concepts were first discovered by astronomers and physicists doing research that appeared to be utterly without any practical significance. Their question was: What is the source of power for the Sun and other stars?

Section 11.1 – The Power Produced by the Sun

Section 11.2 – Energy Sources

Section 11.3 – The Conditions Required for Fusion

Section 11.4 – Proof of Fusion in Stars

Section 11.5 – Stellar Structure

Section 11.6 – The Lifetimes of Stars

Section 11.7 – The Sun—A Typical Star


Chapter Twelve: Star Formation and Evaluation to the Main Sequence

Chapter Synopsis: In this chapter, we first study the clouds of dust and gas, with particular attention to the molecules necessary to the process by which stars form inside these clouds. Then we will look at the currently accepted theory of star formation. Finally, we will examine a variety of observations that show that the theoretical picture we have painted is correct in its general outline. Our goal is to understand how stars form, and what physical processes affect their evolution. Thanks to technological advances in detectors and the capability to place telescopes in space, we are making great progress towards answering these difficult questions.

Section 12.1 – Matter for Star Formation

Section 12.2 – Star-Formation: Theory

Section 12.3 – Star-Formation: Observations

Section 12.4 – A Prominent Region of Star Formation: The Orion Molecular Cloud Complex and Nebula


Chapter Thirteen: Stellar Evolution after the Main Sequence

Chapter Synopsis: In this chapter, we first describe the theoretical picture of stellar evolution that results from extensive computer modeling, and then compare it to a variety of observations.

Section 13.1 – The Mid-Life Evolution of Sunlike Stars

Section 13.2 – The Mid-Life Evolution of Stars Less Massive Than the Sun

Section 13.3 – The Mid-Life Evolution of Stars More Massive Than Eight Solar Masses

Section 13.4 – Pulsating Stars

Section 13.5 – Mass Loss, Binary Stars, and Stellar Evolution

Section 13.6 – The Death of Stars Less Massive Than Eight Solar Masses

Section 13.7 – The Observational Evidence for Stellar Evolution


Chapter Fourteen: Stellar Death and Catastrophes

Chapter Synopsis: In this chapter we will complete the discussion of the life cycle of stars with more than a few solar masses and further examine the evolution of binary stars. Such stars often experience rapid and sometimes violent changes as they age, and they play an important role in our discussion. This chapter also discusses the strangest objects studied by astronomers: neutron stars and black holes.

Section 14.1 – Novae

Section 14.2 – Supernovae

Section 14.3 – Neutron Stars and Pulsars

Section 14.4 – Black Holes

Section 14.5 – Compact Objects in Binary Systems


Chapter Fifteen: The Milky Way - Our Galaxy

Chapter Synopsis: Expanding on the discussion in Chapter 3, we describe attempts to determine the shape and size of our own Milky Way Galaxy along with a more complete description of its components. In an interesting parallel with Copernicus’s dethroning of the Earth, we will see how our true place in our galaxy was found. However, such aspects as structure, size, location and components do not completely describe our galaxy.

Section 15.1 – Characteristics of the Milky Way

Section 15.2 – Characteristics of the Milky Way

Section 15.3 – Interstellar Gas and Dust

Section 15.4 – The Structure of the Milky Way System

Section 15.5 – The Formation and Evolution of the Galaxy

Section 15.6 – The Galactic Magnetic Field

Section 15.7 – Cosmic Rays


Chapter Sixteen: Galaxies

Chapter Synopsis: In addition to learning about individual types of galaxies, we will discover that galaxies are not the largest “things” in the universe. The first structure is our small (few million light-years diameter) Local Group. Hubble’s discovery of a correlation between red shift and distance of galaxies outside the Local Group is described. Still larger are the clusters of galaxies and superclusters made of clusters of galaxies. Along the way we discuss one of the central puzzles of modern astronomy, dark matter which thus far has only revealed itself by its gravitational effects.

Section 16.1 – The Historical Problem of the Nebulae

Section 16.2 – The Morphology of Galaxies

Section 16.3 – Distances of the Galaxies

Section 16.4 – General Galaxy Attributes

Section 16.5 – The Star and Gas Content of Galaxies

Section 16.6 – The Formation and Evolution of Galaxies

Section 16.7 – Clusters of Galaxies

Section 16.8 – Clusters of Clusters: Superclusters

Section 16.9 – Cluster and Supercluster Formation


Chapter Seventeen: Active Galaxies and Quasars

Chapter Synopsis: In this chapter, we describe the observational characteristics of these “active galaxies” and related objects. We also discuss theoretical ideas concerning how the vast amounts of energy associated with many of these systems are produced. In doing so, we will see how astronomers have attempted to produce a unified model for apparently diverse phenomena.

Section 17.1 – Seeing Galaxies in a New Light

Section 17.2 – Other Active Galaxies: Seyfert Galaxies, BL Lac Objects, and Quasars

Section 17.3 – The “Monster” Energy Source for QSOs and AGNs

Section 17.4 – A Unified Model of AGN, BL Lacs and Quasars


Chapter Eighteen: The Origin and Evolution of the Universe

Chapter Synopsis: One of the most remarkable aspects of the study of cosmology is the revolution that has occurred over the last few decades. Because of the advances that have been made, astronomers now think that we have a pretty good idea of the nature of the universe, how it is evolving, and how it will ultimately die.

Section 18.1 – The Four Pillars of the Big Bang

Section 18.2 – Questions about the Big Bang

Section 18.3 – Surprising Mysteries of the Big Bang

Section 18.4 -Multiple Universes?


Chapter Nineteen: Discovering if there is Life Elsewhere in the Universe

Chapter Synopsis: This chapter introduces you to a new science—astrobiology. We will start, as always in this book, with what we know and then see how this guides us in gathering new information. We begin with an exploration of the one example of a world with life that we do know—the Earth—and then infer from that what life on other worlds might be like and how we could detect it. Just as Chapter 1 did, this final chapter will discuss concepts ranging across the scale of astronomical sizes, from the atomic to the galactic.

Section 19.1 – What is Life?

Section 19.2 – The Ingredients for Life

Section 19.3 – The Search for Extra- Terrestrial Life inside Our Solar System

Section 19.4 – The Search for Life Outside Our Solar System

Section 19.5 – The Search for Extraterrestrial Intelligence



About the book

Discovering Astronomy 

Stars, Galaxies, and Universes – 6th Edition

This full book is comprehensive in its coverage of the field and the background information needed to understand astronomy. This  edition is not only up-to-date, but continues and expands upon its unique pedagogical features: an emphasis on understanding the nature of science; its use of in-text inquiries; chapter discoveries. The chapter summaries help emphasize the nature of science by grouping the chapter’s ideas into observations, theory, and conclusions. Concept videos, made specifically for the book to aid understanding physical concepts, are embedded within the text.

New to this edition are Critical Observations, which illustrate specific examples throughout astronomy of how a specific observation allowed astronomers to choose one theory over the competing ideas.

About the authors:

Stephen Shawl

Stephen Shawl brings decades of teaching experience and textbook writing to the newest edition of Discovering Astronomy. His experiences of teaching undergraduate students at all levels were shaped by numerous Chautauqua short courses and other workshops for college teachers that he attended. Starting in the seventies, he integrated peer undergraduate tutors into his teaching of introductory astronomy and continued to use them throughout his career. He was a pioneer at the University of Kansas in the use of student response systems to increase student involvement in their learning. As an extension of his interest in teaching, he was the principal investigator for an astronomy workshop for junior high and middle school science teachers. His textbook writing career began in writing test banks and instructor’s manuals for many editions of an introductory astronomy textbook before he was asked in 1990 to write the third edition of the unique textbook Discovering Astronomy; he has been the first author in producing its later editions. He was a member of the Education Advisory Board of the American Astronomical Society and served as the Chairman of their Working Group on Astronomy Education. Now a professor emeritus at the University of Kansas, during retirement he has taught at the University of Arizona and Pima Community College in Tucson. Educated at the University of California at Berkeley in the early 1960s and the University of Texas at Austin, he received his Ph.D. in 1972. Immediately after receiving his doctorate, he joined the Department of Physics and Astronomy at the University of Kansas. Research interests involved the study of the fundamental properties of globular star clusters, the presence of gas and dust in these clusters, and cool variable stars whose light is sometimes polarized. Stephen Shawl

Emeritus Professor, Department of Physics and Astronomy at the University of Kansas

Gene Byrd

Gene Byrd has been prolific in his writing for students. Starting with one of the original authors of Discovering Astronomy he published a self-paced course used for years at the University of Texas and on-line at the University of Alabama. He is co-author of two senior/graduate level texts Cosmology: Foundations and Frontiers and Paths to Dark Energy: Theory and Observations along with a popular book, The Evolving Universe and the Origin of Life.  He has been honored as a University of Alabama College of Arts and Sciences Distinguished Teaching Fellow. His research interests are the dynamics of galaxies, where he discovered “an inconvenient galaxy” NGC4622, which has inner and outer spiral arms winding in opposite directions, and the effects of dark energy in our local universe. Dr. Byrd served as Secretary and Chair of the American Astronomical Society’s Division on Dynamical Astronomy. He has helped organize several international conferences, the last one in St Petersburg, Russia published as Order and Chaos in Stellar and Dynamical Systems. He received a B.S. in physics from Texas A&M University in 1968 and a PhD in astronomy from the University of Texas at Austin. He became a faculty member at the University of Alabama at Tuscaloosa in 1974, retiring in 2009. Gene Byrd

Emeritus Professor, Department of Physics and Astronomy at the University of Alabama

Susana Deustua

Susana Deustua has been involved in education as faculty, project director, and administrator. She taught at Case Western Reserve University for a year before joining the Lawrence Berkeley National Laboratory as Project Director for the Hands-On Universe education project. As the Director of Education for the American Astronomy Society she was involved in astronomy education nationally before becoming the US Program co-Chair for the International Year of Astronomy 2009, and served on the IAU IYA 2009 Executive Working Group. Susana’s research interests span a broad range from dark energy and supernova cosmology, instrumentation, gas content of elliptical galaxies, precision spectrophotometric calibration, and astronomy education research. She was a staff scientist in the Physics Division as a member of the Lawrence Berkeley Lab’s Supernova Cosmology Project. Susana shared the 2007 Gruber Prize in Cosmology awarded to the Supernova Cosmology Project, the High-Z Supernova Team, Saul Perlmutter and Brian Schmidt for their discovery of Dark Energy. Team members were also recognized through the awarding of the Breakthrough Prize in Physics in 2014. She is currently on the staff at the Space Telescope Science Institute. Broadly educated, she earned her BA in Physics, astronomy and medieval history from Swarthmore College and her Ph.D. in astronomy from the University of Michigan. She held a postdoctoral fellowship at the Lawrence Livermore National Laboratory, followed by an assistant research scientist position at the Space Sciences Laboratory at the University of California-Berkeley. She is a member of the American Astronomical Society, the Astronomical Society of the Pacific, the International Astronomical Union and the American Association of Physics Teachers. Susana Deustua

Associate Scientist, Space Telescope Science Institute

Michael LoPresto

Michael LoPresto is well known the astronomy education community. He has over 20 years of experience teaching introductory astronomy at Henry Ford Community College in Dearborn, Michigan. During that time, he has produced more than 50 publications, many specifically about teaching introductory astronomy, the journals include Astronomy Education ReviewThe Physics TeacherPhysics EducationAmerican Journal of PhysicsMercury, and ASP-Universe in the Classroom. He has made numerous presentations, again many on teaching introductory astronomy, at national and regional meetings, including the Astronomical Society of the Pacific (ASP)-Cosmos in the Classroom Symposiums and the American Association of Physics Teachers (AAPT).  While currently serving as a member of the National Astronomy Education Committee for AAPT and recently appointed a member of the Editorial Board for their journal –The Physics Teacher, he is also a past president of the Michigan Section of the AAPT and is currently organizer of the group’s “Astronomy Arm.” In addition, he is the author of the Astronomy Media Workbook, an Astronomy laboratory manual, an astronomy textbook supplement, Cycles in the Skyand was asked to and wrote a chapter on challenges in astronomy education for the book Science Education Issues and Developments. Finally, he worked with Stephen Shawl in producing a customized edition of the 4th edition of Discovering Astronomy for the University of South Carolina. Michael LoPresto

Lecturer, Department of Astronomy at the University of Michigan

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