Questions for Critical Thinking
Part I. A Sense of the Universe
- The Universe: An Overview
What is cyclical; what is evolving?
- The Early History of Astronomy
What causes retrograde motion? Why are Copernicus's ideas considered
superior to Aristotle's?
- The Origin of Modern Astronomy
How did Galileo's observations of Venus confirm Copernican theory?
- Light and the Spectrum
How can the same gas provide both emission lines and absorption lines?
What do spectral lines tell us?
- Telescopes and Spacecraft
How do astronomers circumvent the limitations of the atmosphere for
resolution and spectral range?
- The Sky and the Calendar
What causes the seasons? Why are solar days 4 minutes longer than
Part II. The Solar System
- 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?
- Our Earth
Why are there tides, and how does the tidal force differ from the
- 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?
What does the existence of scarps tell us about Mercury's history and
How is the greenhouse effect on Venus linked to calculations of its
Why is Mars's sky pink while the Earth's is blue? Why does Mars show
seasonal surface changes?
How does the Coriolis force cause the Great Red Spot? Why isn't the
Coriolis force considered a real force?
What relation are Saturn's rings to Roche's limit and to tidal forces?
Why does Uranus's rotation help us understand Earth's weather? Why
are Uranus's rings so narrow?
Why does Neptune look blue? How does Neptune's magnetic field compare
Is Pluto a planet?
- New Planets
Since we can't see the exoplanets directly, how do we convince
ourselves that they are there?
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?
- Meteorites and Asteroids
Why do we find more iron than stony meteorites on Earth? Why are the
gaps in the asteroid belt?
- Life in the Universe
Have signs of life on Mars been discovered? Is it worthwhile to
undertake SETI programs?
Part III. The Sun
- 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?
- 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
- 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?
- 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
- 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
Part V. Stellar Evolution
- 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
- 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?
How do we distinguish observationally between two types of supernova?
How are the two types of supernova fundamentally different?
- 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?
- 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
Part VI. The Milky Way Galaxy
- 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?
- 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
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?
- 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?
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?
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
- 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