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 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 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 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 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 Synopsis: In this chapter we will look at the overall structure of the Solar System (we defer the details to Chapters 8 to 10). We will find some striking patterns that can lead us to an understanding about how the Solar System formed. We will discuss some of the hypotheses of Solar System formation and see how well each fits the observable data. Once we have done this we will compare our own solar system to known planetary systems elsewhere in the universe.

Section 6.1 – An Overview of the Solar System

Section 6.2 – Observations: Orbital Patterns

Section 6.3 – The Distribution of Angular Momentum

Section 6.4 – Hypotheses of the Origin of the Solar System

Section 6.5 – Modern Ideas

Section 6.6 – Other Planetary Systems

Section 7.1 – Pluto and the Trans-Neptunian Objects

Section 7.2 – Comets

Section 7.3 – Asteroids

Section 7.4 – Meteors, Meteor Showers, and Meteorites

Section 7.5 – Interplanetary Dust

Section 7.6 – Meteorites and the Early Solar System

Chapter Synopsis: Earth is a planet, circling the Sun in its own time like all the other planets. Our presence on it makes the Earth of special interest to us. It makes sense to begin our study of planets by learning some of the basic facts about our own home planet as well as the variety of processes that have made the Earth the way it is.

Section 8.1 – Earth as an Astronomical Body

Section 8.2 – Earth’s Interior

Section 8.3 – Earth’s Surface

Section 8.4 – Earth’s Atmosphere

Section 8.5 – Earth’s Magnetism

Section 8.6 – The Moon: Large-Scale Characteristics

Chapter Synopsis: In this chapter, we study the terrestrial planets from the viewpoint of comparative planetology, comparing and contrasting them with each other. We use Earth and the Moon as the standards of comparison, simply because we know more about them and the processes that determined the way they are.

Section 9.1 – Introduction to the Terrestrial Planets

Section 9.2 – Large-Scale Characteristics

Section 9.3 – Atmospheres

Section 9.4 – Surfaces

Section 9.5 – Interiors

Section 9.6 – Moons

Section 9.7 – Evolutionary Comparison

Chapter Synopsis: In this chapter you will learn about some of the exciting results of recent explorations, and you will see that processes studied in earlier chapters are applicable to each of the Jovian planets and their moons.

Section 10.1 – Introduction

Section 10.2 – Large-Scale Characteristics

Section 10.3 – Atmospheres

Section 10.4 – Planetary Interiors

Section 10.5 – Planetary Interiors

Section 10.6 – Planetary Rings

Section 10.7 – Future Studies of the Jovian Planets and Moons

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 11.1 – Light as a Ray

Section 11.2 – Light as a Wave

Section 11.3 – Light as a Stream of Particles

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 12.1 – The Formation of Images

Section 12.2 – Telescopes

Section 12.3 – Comparing Reflecting and Refracting Telescopes

Section 12.4 – Reflecting Telescopes of Various Types

Section 12.5 –  The Telescopes of the Future

Section 12.6 – Detectors and Instruments

Section 12.7 – Radio Astronomy

Section 12.8 – Optical and Radio Observatory Sites

Section 12.9 – Beyond Optical and Radio Astronomy

Section 12.10 – NASA’s Great Observatories

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 13.1 – Observations of Spectra

Section 13.2 – Understanding Spectra

Section 13.3 – Applications of Spectroscopy

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 21) 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 18), and their membership in clusters of stars (Chapters 15 and 18). 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 14.1 – Classification of Stellar Spectra

Section 14.2 – The Cosmic Abundance of the Chemical Elements

Section 14.3 – The Doppler Effect

Section 14.4 – What We Can Learn from Spectral Lines

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 15.1 – Distance Measurements

Section 15.2 – Binary Stars and Stellar Masses

Section 15.3 – Binary Stars and Other Stellar Properties

Section 15.4 – The Hertzsprung-Russell Diagram

Section 15.5 – Main-Sequence, Giant, Supergiant, and White Dwarf Stars

Section 15.6 – Explanation of the Main Sequence

Section 15.7 – Stellar Distances and the H-R Diagram

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 16.1 – The Power Produced by the Sun

Section 16.2 – Energy Sources

Section 16.3 – The Conditions Required for Fusion

Section 16.4 – Proof of Fusion in Stars

Section 16.5 – Stellar Structure

Section 16.6 – The Lifetimes of Stars

Section 16.7 – The Sun—A Typical Star

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 17.1 – Matter for Star Formation

Section 17.2 – Star-Formation: Theory

Section 17.3 – Star-Formation: Observations

Section 17.4 – A Prominent Region of Star Formation: The Orion Molecular Cloud Complex and Nebula

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 18.1 – The Mid-Life Evolution of Sunlike Stars

Section 18.2 – The Mid-Life Evolution of Stars Less Massive Than the Sun

Section 18.3 – The Mid-Life Evolution of Stars More Massive Than Eight Solar Masses

Section 18.4 – Pulsating Stars

Section 18.5 – Mass Loss, Binary Stars, and Stellar Evolution

Section 18.6 – The Death of Stars Less Massive Than Eight Solar Masses

Section 18.7 – The Observational Evidence for Stellar Evolution 

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 19.1 – Novae

Section 19.2 – Supernovae

Section 19.3 – Neutron Stars and Pulsars

Section 19.4 – Black Holes

Section 19.5 – Compact Objects in Binary Systems

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 20.1 – Characteristics of the Milky Way

Section 20.2 – Characteristics of the Milky Way

Section 20.3 – Interstellar Gas and Dust

Section 20.4 – The Structure of the Milky Way System

Section 20.5 – The Formation and Evolution of the Galaxy

Section 20.6 – The Galactic Magnetic Field

Section 20.7 – Cosmic Rays

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 21.1 – The Historical Problem of the Nebulae

Section 21.2 – The Morphology of Galaxies

Section 21.3 – Distances of the Galaxies

Section 21.4 – General Galaxy Attributes

Section 21.5 – The Star and Gas Content of Galaxies

Section 21.6 – The Formation and Evolution of Galaxies

Section 21.7 – Clusters of Galaxies

Section 21.8 – Clusters of Clusters: Superclusters

Section 21.9 – Cluster and Supercluster Formation

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 22.1 – Seeing Galaxies in a New Light

Section 22.2 – Other Active Galaxies: Seyfert Galaxies, BL Lac Objects, and Quasars

Section 22.3 – The “Monster” Energy Source for QSOs and AGNs

Section 22.4 – A Unified Model of AGN, BL Lacs and Quasars

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 23.1 – The Four Pillars of the Big Bang

Section 23.2 – Questions about the Big Bang

Section 23.3 – Surprising Mysteries of the Big Bang

Section 23.4 -Multiple Universes?

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 24.1 – What is Life?

Section 24.2 – The Ingredients for Life

Section 24.3 – The Search for Extra- Terrestrial Life inside Our Solar System

Section 24.4 – The Search for Life Outside Our Solar System

Section 24.5 – The Search for Extraterrestrial Intelligence