Part I. A Sense of the Universe

1. The Universe: An Overview
   What is cyclical; what is evolving?
2. The Early History of Astronomy
   What causes retrograde motion? Why are Copernicus's ideas considered superior to Aristotle's?
3. The Origin of Modern Astronomy
   How did Galileo's observations of Venus confirm Copernican theory?
4. Light and the Spectrum
   How can the same gas provide both emission lines and absorption lines? What do spectral lines tell us?
5. Telescopes and Spacecraft
   How do astronomers circumvent the limitations of the atmosphere for resolution and spectral range?
6. The Sky and the Calendar
   What causes the seasons? Why are solar days 4 minutes longer than sidereal days?

   Part II. The Solar System

7. The Structure and Origin of the Solar System
   What causes the phases of the Moon? What role did angular momentum play in forming the planets?
8. Our Earth
   Why are there tides, and how does the tidal force differ from the gravitational force?
   
9. Our Moon
   How do studies of craters reveal the age of portions of the lunar surface? How have instruments brought to the Moon by astronauts revealed the lunar interior?
   
10. Mercury
    What does the existence of scarps tell us about Mercury's history and why?
    
11. Venus
    How is the greenhouse effect on Venus linked to calculations of its equilibrium temperature?
    
12. Mars
    Why is Mars's sky pink while the Earth's is blue? Why does Mars show seasonal surface changes?
    
13. Jupiter
    How does the Coriolis force cause the Great Red Spot? Why isn't the Coriolis force considered a real force?
14. Saturn
    What relation are Saturn's rings to Roche's limit and to tidal forces?
15. Uranus
    Why does Uranus's rotation help us understand Earth's weather? Why are Uranus's rings so narrow?
    
16. Neptune
    Why does Neptune look blue? How does Neptune's magnetic field compare with Earth's?
    
17. Pluto
    Is Pluto a planet?
    
18. New Planets
    Since we can't see the exoplanets directly, how do we convince ourselves that they are there?
    
19. Comets
    Why do comets provide a link with the early solar system? Why do comets have several tails? What is the nucleus of a comet link and how do we know?
    
20. Meteorites and Asteroids
    Why do we find more iron than stony meteorites on Earth? Why are the gaps in the asteroid belt?
    
21. Life in the Universe
    Have signs of life on Mars been discovered? Is it worthwhile to undertake SETI programs?

    Part III. The Sun

22. Our Star, the Sun
    How does helioseismology tell us about the sun's interior? How do we get three-dimensional information about the solar atmosphere?
23. The Sun and the Earth
    Why does the sunspot cycle give a butterfly diagram? Why isn't the solar constant constant?

    Part IV. The Stars

24. Ordinary Stars
    How are Wien's law, the Stefan-Boltzmann law, and Planck's law related? How are Planck curves for different temperatures related? Why does the Balmer series converge?
    
25. Stellar Distances and Motions
    Why does parallax reveal a star's distance? Why does color index reveal a star's temperature? Why does the Hertzsprung-Russell diagram take its form? Why does the Doppler effect reveal radial but not transverse velocities?
    
26. Doubles, Variables, and Clusters
    How can the same set of stars appear as a visual, a spectroscopic, or an eclipsing binary. How do Cepheid variables reveal the distances of galaxies? How do we know that we are not in the center of our galaxy? How do their Hertzsprung-Russell diagrams reveal the relative ages of galactic clusters? Why do all globular clusters have similar Hertzsprung-Russell diagrams?

    Part V. Stellar Evolution

27. The Birth, Youth, and Middle Age of Stars How are astronomers finding signs of starbirth and of young stars? What cycles fuel the stars? What is the significance of the solar-neutrino problem?
    
28. The Death of Stars Like the Sun
    What gives planetary nebulae their shapes? How do we tell the age of stars from their positions in the Hertzsprung-Russell diagram? Why don't white dwarfs collapse?
    
29. Supernovae
    How do we distinguish observationally between two types of supernova? How are the two types of supernova fundamentally different?
30. Pulsars and Other Neutron Stars
    Why don't neutron stars collapse? Why have astronomers concluded that pulsars are neutron stars? How have pulsars tested Einstein's theory of gravitational emission?
    
31. Stellar Black Holes
    How do rotating black holes differ from nonrotating black holes? How do we conclude that an object is a black hole? How can mini black holes radiate?

    Part VI. The Milky Way Galaxy

32. The Structure of Our Galaxy
    Why have astronomers concluded that our galaxy has a giant black hole at its nucleus? What are the sources of the gamma-ray bursts? Why don't the Milky Way Galaxy's spiral arms wind up?
33. Between the Stars
    How has the spin-flip of hydrogen revealed the structure of our galaxy? How do complicated molecules form in sufficient abundance to be detected? What is the relation of molecular clouds and star formation? Why are infrared observations particularly useful for studying star formation?
    

    Part VII. Galaxies and Cosmology

34. Galaxies
    How do spectra show that certain galaxies have giant black holes in them? What are some results of galaxy interactions? Why do radio galaxies have lobes and jets? How does aperture synthesis work? What are the advantages of very-long-baseline interferometry?
35. The Expanding Universe
    Why does Hubble's law indicate that the universe is expanding? What are key steps in the cosmic distance ladder that led to the Hubble Space Telescope's key project on the cosmic distance scale? What might dark matter be made of?
    
36. Quasars
    Why do almost all astronomers conclude that quasars are very far away? How has the energy problem for quasars been resolved? What contribution has Hubble Space Telescope images made to quasar studies? How can superluminal velocities appear to arise? How does gravitational lensing work?
    
37. Cosmology
    Why does the sky appear uniformly dark at night between the stars? Will the universe expand forever or eventually contract? How do galaxies evolve? What does the cosmic background radiation reveal about the existence of the big bang? What do ripples in the cosmic background radiation reveal about galaxy formation? What are the first, second, and third peaks showing and what are the axes of their graph? How does their graph compare with a Planck curve or differ from it?
    
38. The Past and Future of the Universe
    How do studies of cosmic deuterium reveal information about the future of the universe? How much dark matter is there in the universe? How can the same types of quarks make both neutrons and protons? Will string theory prove to be a Theory of Everything? Did the universe go through an inflationary era? What has the Hubble Deep Field revealed about the early times of the universe? How did structure arise in the universe?