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Welcome to Astronomy 2e, an OpenStax resource. This textbook was written to increase student access to high-quality learning materials, maintaining highest standards of academic rigor at little to no cost.

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About Astronomy 2e

Astronomy 2e is written in clear non-technical language, with the occasional touch of humor and a wide range of clarifying illustrations. It has many analogies drawn from everyday life to help non-science majors appreciate, on their own terms, what our modern exploration of the universe is revealing. The book can be used for either a one-semester or two-semester introductory course (bear in mind, you can customize your version and include only those chapters or sections you will be teaching.) It is made available free of charge in electronic form (and low cost in printed form) to students around the world.

Coverage and scope

Astronomy 2e was written by its three senior authors (see below) and was updated, reviewed, and vetted by a wide range of astronomers and astronomy educators in a strong community effort. It is designed to meet scope and sequence requirements of introductory astronomy courses nationwide.

  • Chapter 1: Science and the Universe: A Brief Tour
  • Chapter 2: Observing the Sky: The Birth of Astronomy
  • Chapter 3: Orbits and Gravity
  • Chapter 4: Earth, Moon, and Sky
  • Chapter 5: Radiation and Spectra
  • Chapter 6: Astronomical Instruments
  • Chapter 7: Other Worlds: An Introduction to the Solar System
  • Chapter 8: Earth as a Planet
  • Chapter 9: Cratered Worlds
  • Chapter 10: Earthlike Planets: Venus and Mars
  • Chapter 11: The Giant Planets
  • Chapter 12: Rings, Moons, and Pluto
  • Chapter 13: Comets and Asteroids: Debris of the Solar System
  • Chapter 14: Cosmic Samples and the Origin of the Solar System
  • Chapter 15: The Sun: A Garden-Variety Star
  • Chapter 16: The Sun: A Nuclear Powerhouse
  • Chapter 17: Analyzing Starlight
  • Chapter 18: The Stars: A Celestial Census
  • Chapter 19: Celestial Distances
  • Chapter 20: Between the Stars: Gas and Dust in Space
  • Chapter 21: The Birth of Stars and the Discovery of Planets outside the Solar System
  • Chapter 22: Stars from Adolescence to Old Age
  • Chapter 23: The Death of Stars
  • Chapter 24: Black Holes and Curved Spacetime
  • Chapter 25: The Milky Way Galaxy
  • Chapter 26: Galaxies
  • Chapter 27: Active Galaxies, Quasars, and Supermassive Black Holes
  • Chapter 28: The Evolution and Distribution of Galaxies
  • Chapter 29: The Big Bang
  • Chapter 30: Life in the Universe
  • Appendix A: How to Study for Your Introductory Astronomy Course
  • Appendix B: Astronomy Websites, Pictures, and Apps
  • Appendix C: Scientific Notation
  • Appendix D: Units Used in Science
  • Appendix E: Some Useful Constants for Astronomy
  • Appendix F: Physical and Orbital Data for the Planets
  • Appendix G: Selected Moons of the Planets
  • Appendix H: Upcoming Total Eclipses
  • Appendix I: The Nearest Stars, Brown Dwarfs, and White Dwarfs
  • Appendix J: The Brightest Twenty Stars
  • Appendix K: The Chemical Elements
  • Appendix L: The Constellations
  • Appendix M: Star Charts and Sky Event Resources

Currency and accuracy

Astronomy 2e has information and images from the LIGO and VIRGO gravitational-wave detectors, the Perseverance/Ingenuity mission to Mars, the Juno mission to Jupiter, and many other recent projects in astronomy. The discussion of exoplanets has been updated with recent information—indicating not just individual examples, but trends in what sorts of planets seem to be most common. Black holes receive their own chapter, and the role of supermassive black holes in active galaxies and galaxy evolution is clearly explained. Chapters have been reviewed by subject-matter experts for accuracy and currency.


Because there are many different ways to teach introductory astronomy, we have made the text as flexible as we could. Math examples are shown in separate sections throughout, so that you can leave out the math or require it as you deem best. Each section of a chapter treats a different aspect of the topic being covered; a number of sections could be omitted in shorter overview courses and can be included where you need more depth. And, as we have already discussed, you can customize the book in a variety of ways that have never been possible in traditional textbooks.

Student-centered focus

This book is written to help students understand the big picture rather than get lost in random factoids to memorize. The language is accessible and inviting. Helpful diagrams and summary tables review and encapsulate the ideas being covered. Each chapter contains interactive group activities you can assign to help students work in teams and pool their knowledge.

Interactive online resources

Interesting “Links to Learning” are scattered throughout the chapters, which direct students to online animations, short videos, or enrichment readings to enhance their learning. Also, the resources listed at the end of each chapter include links to websites and other useful educational videos.

Feature boxes that help students think outside the box

A variety of feature boxes within the chapters connect astronomy to the students’ other subjects and humanize the face of astronomy by highlighting the lives of the men and women who have been key to its progress. Besides the math examples that we’ve already mentioned, the boxes include:

  • Making Connections. This feature connects the chapter topic to students’ experiences with other fields, from poetry to engineering, popular culture, and natural disasters.
  • Voyagers in Astronomy. This feature presents brief and engaging biographies of the people behind historically significant discoveries, as well as emerging research.
  • Astronomy Basics. This feature explains basic science concepts that we often (incorrectly) assume students know from earlier classes.
  • Seeing for Yourself. This feature provides practical ways that students can make astronomical observations on their own.

End-of-chapter materials to extend students’ learning

  • Chapter Summaries. Summaries give the gist of each section for easy review.
  • For Further Exploration. This section offers a list of suggested articles, websites, and videos so students can delve into topics of interest, whether for their own learning, for homework, extra credit, or papers.
  • Review Questions. Review questions allow students to show you (or themselves) how well they understood the chapter.
  • Thought Questions. Thought questions help students assess their learning by asking for critical reflection on principles or ideas in the chapter.
  • Figuring For Yourself. Mathematical questions, using only basic algebra and arithmetic, allow students to apply the math principles given in the example boxes throughout the chapter.
  • Collaborative Group Activities. This section suggests ideas for group discussion, research, or reports.

Beautiful art program

Our comprehensive art program is designed to enhance students’ understanding of concepts through clear and effective illustrations, diagrams, and photographs. Here are a few examples.

Model of a Pulsar. In this illustration the Earth is drawn below center, in the path of an approaching “Beam of particles and radiation”. The pulsar, labeled “Neutron star”, is drawn at upper right as a blue sphere. Its rotation axis is drawn vertically upward, with a counter-clockwise arrow around it indicating the direction of rotation. The magnetic field lines are drawn in a plane perpendicular to the rotation axis as concentric red ellipses on either side of the star. The field lines intersect the surface of the star at the “North magnetic pole”, which faces Earth, and the “South magnetic pole”, which faces toward upper right. The beam of radiation is emitted from the poles of the magnetic field, and extend toward upper right and lower left.
Figure 1 How a Pulsar Beam Sweeps over Earth.
Map of the Milky Way Galaxy. Over-plotted on this data-based illustration of the Milky Way is a coordinate system centered on the Sun, which is located about half way from the center and the bottom of the image. It is a polar coordinate system, with zero degrees straight up from the Sun, 90O to the left, 180O straight down and 270O to the right. Distances are shown as circles of increasing radius centered on the Sun. Distances from 15,000 ly to 75,000 ly are indicated in increments of 5,000 ly. Moving outward from the Sun along the zero degree line are the “Near 3kpc Arm”, “Far 3 kpc Arm” and the “Sagittarius Arm”. Moving outward from the Sun along the 330O line (to the right of zero) are the “Norma Arm” and the “Scutum-Centaurus Arm”. Moving outward from the Sun along the 90O line are are the: “Orion Spur”, “Perseus Arm” and the “Outer Arm”.
Figure 2 Structure of the Milky Way Galaxy.
A graph of solar masses in the Interstellar Graveyard
Figure 3 Masses in the Stellar Graveyard.
A global color image of Pluto, showing a dark area in the lower left covered with impact craters, and a larger light area in the center and lower right that is flat.
Figure 4 Pluto Close Up.

Answers to Questions in the Book

In order to allow instructors as much flexibility as possible, answers are provided only to instructors via the instructor resources. Due to the high variability of responses, aswers to Collaborative Group Activities are not provided.

Additional resources

Student and instructor resources

We’ve compiled additional resources for both students and instructors, including Getting Started Guides, PowerPoint slides, and an instructor answer guide. Instructor resources require a verified instructor account, which you can apply for when you log in or create your account on Take advantage of these resources to supplement your OpenStax book.

Community Hubs

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To reach the Community Hubs, visit

Partner resources

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About the authors

Senior contributing authors

Senior contributing authors: Andrew Fraknoi (left), David Morrison (center), Sidney C. Wolff (right)
Figure 5 Senior contributing authors: Andrew Fraknoi (left), David Morrison (center), Sidney C. Wolff (right)

Andrew Fraknoi, Fromm Institute, University of San Francisco
Andrew Fraknoi retired as Chair of the Astronomy Department at Foothill College in 2017 and now teaches courses for older adults at the University of San Francisco and San Francisco State University. He served as the Executive Director of the Astronomical Society of the Pacific from 1978–1992. His work with the society included editing Mercury Magazine, the Universe in the Classroom newsletter, and Astronomy Beat. He is editor/co-author of The Universe at Your Fingertips 2.0, a collection of teaching activities, and co-author of Solar Science, a book for middle-school teachers. He was also co-author of a syndicated newspaper column on astronomy, and appears regularly on local and national radio. With Sidney Wolff, he was founder of the refereed journal, Astronomy Education Review. In addition, he has organized six national symposia on teaching introductory astronomy, and for 10 years, has led the AAS Ambassadors workshops, training young astronomers to be better at outreach. He received the AAS Education Award, the Klumpke-Roberts Prize of the ASP, the Gemant Prize of the American Institute of Physics, and the Faraday Award of the NSTA.

David Morrison, NASA (Emeritus) and SETI Institute
David Morrison received his PhD in astronomy from Harvard, where he was one of Carl Sagan’s graduate students. He is a founder of the field of astrobiology and is known for research on small bodies in the solar system (Asteroid 2410 Morrison is named for him). He spent his early career at University of Hawaii’s Institute for Astronomy, where he was Director of the IRTF at Maunakea Observatory. Morrison has held senior NASA positions including Director of Space Research at Ames Research Center, Chief of the Space Science Division, and founding Director of the Lunar Science Institute. He’s been on science teams for the Voyager, Galileo, and Kepler missions, and he received NASA Outstanding Leadership Medals and Exceptional Achievement Medal. His contributions to public understanding of science have been recognized by education prizes from the Astronomical Society of the Pacific, the American Astronomical Society, and NASA. Committed to the struggle against pseudoscience, he serves as Contributing Editor of Skeptical Inquirer.

Sidney C. Wolff, NOIRLab (Emerita)
After receiving her PhD from the UC Berkeley, Dr. Wolff was involved with the astronomical development of Maunakea. In 1984, she became the Director of Kitt Peak National Observatory, and was director of National Optical Astronomy Observatory. She led the design and development phases of the Gemini Observatory and the Rubin Observatory. Most recently, she has worked on plans for user support for the next generation of large ground-based telescopes. Dr. Wolff has published over ninety refereed papers on star formation and stellar atmospheres. She has served as President of the AAS and the ASP. Her book, The Boundless Universe: Astronomy in the New Age of Discovery, won the 2016 IPPY (Independent Publisher Book Awards) Silver Medal in Science.

All three senior contributing authors have received the Education Prize of the American Astronomical Society and have had an asteroid named after them by the International Astronomical Union. They have worked together on a series of astronomy textbooks over the past two decades.

Contributing authors

John Beck, Stanford University
Susan D. Benecchi, Planetary Science Institute
John Bochanski, Rider University
Howard Bond, Pennsylvania State University, Emeritus, Space Telescope Science Institute
Jennifer Carson, Occidental College
Bryan Dunne, University of Illinois at Urbana-Champaign
Martin Elvis, Harvard-Smithsonian Center for Astrophysics
Debra Fischer, Yale University
Heidi Hammel, Association of Universities for Research in Astronomy
Tori Hoehler, NASA Ames Research Center
Douglas Ingram, Texas Christian University
Steven Kawaler, Iowa State University
Lloyd Knox, University of California, Davis
Mark Krumholz, Australian National University
James Lowenthal, Smith College
Geoff Mathews, Foothill College
Siobahn Morgan, University of Northern Iowa
Daniel Perley, California Institute of Technology
Claire Raftery, National Solar Observatory
Deborah Scherrer, retired, Stanford University
Phillip Scherrer, Stanford University
Sanjoy Som, Blue Marble Space Institute of Science, NASA Ames Research Center
Wes Tobin, Indiana University East
William H. Waller, retired, Tufts University, Rockport (MA) Public Schools
Todd Young, Wayne State College


Elisabeth R. Adams, Planetary Science Institute
Alfred N. Alaniz, San Antonio College
Charles Allison, Texas A&M University–Kingsville
Douglas Arion, Carthage College
Timothy Barker, Wheaton College
Marshall Bartlett, The Hockaday School
Charles Benesh, Wesleyan College
Gerald B. Cleaver, Baylor University
Kristi Concannon, King’s College
Anthony Crider, Elon University
Scott Engle, Villanova University
Matthew Fillingim, University of California, Berkeley
Robert Fisher, University of Massachusetts, Dartmouth
Carrie Fitzgerald, Montgomery College
Christopher Fuse, Rollins College
Shila Garg, Emeritus, The College of Wooster
Richard Gelderman, Western Kentucky University
Lee Hartman, University of Michigan
Beth Hufnagel, Anne Arundel Community College
Francine Jackson, Brown University
Joseph Jensen, Utah Valley University
John Kielkopf, University of Louisville
James C. Lombardi, Jr., Allegheny College
Amy Lovell, Agnes Scott College
Charles Niederriter, Gustavus Adolphus College
Richard Olenick, University of Dallas
Matthew Olmstead, King’s College
Zoran Pazameta, Eastern Connecticut State University
David Quesada, Saint Thomas University
Valerie A. Rapson, Dudley Observatory
Joseph Ribaudo, Utica College
Dean Richardson, Xavier University of Louisiana
Andrew Rivers, Northwestern University
Marc Sher, College of William & Mary
Christopher Sirola, University of Southern Mississippi
Ran Sivron, Baker University
J. Allyn Smith, Austin Peay State University
Jason Smolinski, Calvin College
Michele Thornley, Bucknell University
Richard Webb, Union College
Terry Willis, Chesapeake College
David Wood, San Antonio College
Jeremy Wood, Hazard Community and Technical College
Jared Workman, Colorado Mesa University
Kaisa E. Young, Nicholls State University

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