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Astronomy 2e

OpenStax · 199 sections in 31 chapters. Each section is its own page.

Front matter

• Preface

• How to Study for an Introductory Astronomy Class

• Astronomy Websites, Images, and Apps

• Scientific Notation

• Units Used in Science

• Some Useful Constants for Astronomy

• Physical and Orbital Data for the Planets

• Selected Moons of the Planets

• Future Total Eclipses

• The Nearest Stars, Brown Dwarfs, and White Dwarfs

• The Brightest Twenty Stars

• The Chemical Elements

• The Constellations

• Star Chart and Sky Event Resources

Science and the Universe: A Brief Tour

• Introduction

• The Nature of Astronomy

• The Nature of Science

• The Laws of Nature

• Numbers in Astronomy

• Consequences of Light Travel Time

• A Tour of the Universe

• The Universe on the Large Scale

• The Universe of the Very Small

• A Conclusion and a Beginning

Observing the Sky: The Birth of Astronomy

• Thinking Ahead

• The Sky Above

• Ancient Astronomy

• Astrology and Astronomy

• The Birth of Modern Astronomy

Orbits and Gravity

• Thinking Ahead

• The Laws of Planetary Motion

• Newton’s Great Synthesis

• Newton’s Universal Law of Gravitation

• Orbits in the Solar System

• Motions of Satellites and Spacecraft

• Gravity with More Than Two Bodies

Earth, Moon, and Sky

• Thinking Ahead

• Earth and Sky

• The Seasons

• Keeping Time

• The Calendar

• Phases and Motions of the Moon

• Ocean Tides and the Moon

• Eclipses of the Sun and Moon

Radiation and Spectra

• Thinking Ahead

• The Behavior of Light

• The Electromagnetic Spectrum

• Spectroscopy in Astronomy

• The Structure of the Atom

• Formation of Spectral Lines

• The Doppler Effect

Astronomical Instruments

• Thinking Ahead

• Telescopes

• Telescopes Today

• Visible-Light Detectors and Instruments

• Radio Telescopes

• Observations outside Earth’s Atmosphere

• The Future of Large Telescopes

Other Worlds: An Introduction to the Solar System

• Thinking Ahead

• Overview of Our Planetary System

• Composition and Structure of Planets

• Dating Planetary Surfaces

• Origin of the Solar System

Earth as a Planet

• Thinking Ahead

• The Global Perspective

• Earth’s Crust

• Earth’s Atmosphere

• Life, Chemical Evolution, and Climate Change

• Cosmic Influences on the Evolution of Earth

Cratered Worlds

• Thinking Ahead

• General Properties of the Moon

• The Lunar Surface

• Impact Craters

• The Origin of the Moon

• Mercury

Earthlike Planets: Venus and Mars

• Thinking Ahead

• The Nearest Planets: An Overview

• The Geology of Venus

• The Massive Atmosphere of Venus

• The Geology of Mars

• Water and Life on Mars

• Divergent Planetary Evolution

The Giant Planets

• Thinking Ahead

• Exploring the Outer Planets

• The Giant Planets

• Atmospheres of the Giant Planets

Rings, Moons, and Pluto

• Thinking Ahead

• Ring and Moon Systems Introduced

• The Galilean Moons of Jupiter

• Titan and Triton

• Pluto and Charon

• Planetary Rings (and Enceladus)

Comets and Asteroids: Debris of the Solar System

• Thinking Ahead

• Asteroids

• Asteroids and Planetary Defense

• The “Long-Haired” Comets

• The Origin and Fate of Comets and Related Objects

Cosmic Samples and the Origin of the Solar System

• Thinking Ahead

• Meteors

• Meteorites: Stones from Heaven

• Formation of the Solar System

• Comparison with Other Planetary Systems

• Planetary Evolution

The Sun: A Garden-Variety Star

• Thinking Ahead

• The Structure and Composition of the Sun

• The Solar Cycle

• Solar Activity above the Photosphere

• Space Weather

The Sun: A Nuclear Powerhouse

• Thinking Ahead

• Sources of Sunshine: Thermal and Gravitational Energy

• Mass, Energy, and the Theory of Relativity

• The Solar Interior: Theory

• The Solar Interior: Observations

Analyzing Starlight

• Thinking Ahead

• The Brightness of Stars

• Colors of Stars

• The Spectra of Stars (and Brown Dwarfs)

• Using Spectra to Measure Stellar Radius, Composition, and Motion

The Stars: A Celestial Census

• Thinking Ahead

• A Stellar Census

• Measuring Stellar Masses

• Diameters of Stars

• The H–R Diagram

Celestial Distances

• Thinking Ahead

• Fundamental Units of Distance

• Surveying the Stars

• Variable Stars: One Key to Cosmic Distances

• The H–R Diagram and Cosmic Distances

Between the Stars: Gas and Dust in Space

• Thinking Ahead

• The Interstellar Medium

• Interstellar Gas

• Cosmic Dust

• Cosmic Rays

• The Life Cycle of Cosmic Material

• Interstellar Matter around the Sun

The Birth of Stars and the Discovery of Planets outside the Solar System

• Thinking Ahead

• Star Formation

• The H–R Diagram and the Study of Stellar Evolution

• Evidence That Planets Form around Other Stars

• Planets beyond the Solar System: Search and Discovery

• Exoplanets Everywhere: What We Are Learning

• New Perspectives on Planet Formation

Stars from Adolescence to Old Age

• Thinking Ahead

• Evolution from the Main Sequence to Red Giants

• Star Clusters

• Checking Out the Theory

• Further Evolution of Stars

• The Evolution of More Massive Stars

The Death of Stars

• Thinking Ahead

• The Death of Low-Mass Stars

• Evolution of Massive Stars: An Explosive Finish

• Supernova Observations

• Pulsars and the Discovery of Neutron Stars

• The Evolution of Binary Star Systems

• The Mystery of the Gamma-Ray Bursts

Black Holes and Curved Spacetime

• Thinking Ahead

• Introducing General Relativity

• Spacetime and Gravity

• Tests of General Relativity

• Time in General Relativity

• Black Holes

• Evidence for Black Holes

• Gravitational Wave Astronomy

The Milky Way Galaxy

• Thinking Ahead

• The Architecture of the Galaxy

• Spiral Structure

• The Mass of the Galaxy

• The Center of the Galaxy

• Stellar Populations in the Galaxy

• The Formation of the Galaxy

Galaxies

• Thinking Ahead

• The Discovery of Galaxies

• Types of Galaxies

• Properties of Galaxies

• The Extragalactic Distance Scale

• The Expanding Universe

Active Galaxies, Quasars, and Supermassive Black Holes

• Thinking Ahead

• Quasars

• Supermassive Black Holes: What Quasars Really Are

• Quasars as Probes of Evolution in the Universe

The Evolution and Distribution of Galaxies

• Thinking Ahead

• Observations of Distant Galaxies

• Galaxy Mergers and Active Galactic Nuclei

• The Distribution of Galaxies in Space

• The Challenge of Dark Matter

• The Formation and Evolution of Galaxies and Structure in the Universe

The Big Bang

• Thinking Ahead

• The Age of the Universe

• A Model of the Universe

• The Beginning of the Universe

• The Cosmic Microwave Background

• What Is the Universe Really Made Of?

• The Inflationary Universe

• The Anthropic Principle

Life in the Universe

• Thinking Ahead

• The Cosmic Context for Life

• Astrobiology

• Searching for Life beyond Earth

• The Search for Extraterrestrial Intelligence

Attribution. Astronomy 2e, OpenStax, Rice University, and the contributing authors credited in the book. Licensed under Creative Commons Attribution 4.0 International. Source revision 63157f370b of openstax/osbooks-astronomy (2026-02-02). CC BY 4.0. Original source ↗. Text edition of a pinned CC BY 4.0 source revision of the OpenStax book, converted from CNXML by the EvidenceHelix importer. Original prose, learning objectives, tables, exercises, glossary and captions are preserved; images are not copied (figures link to the original source and keep their credits). No new content was added. Later revisions of this book can carry different licence terms and are not used.