Discovering the Cosmos

By R.C. Bless
University of Wisconsin, Madison


1. Introduction

The Astronomy You Will Learn
Cosmology: The Beginnings Through Newton (Part I)
The Life and Death of Stars (Part II)
Cosmology: Herschel to the Present (Part III)
Worlds Beyond the Earth (Part IV)
Astronomy as a Science
Suggestions for Further Reading

I: Cosmology: The Beginnings Through Newton

2. The Naked-Eye Sky

The Size of the Solar System
The Nearest Star
Motions of the Sun and Stars
Some Useful Terms
Motion of the Sun
Motions of the Star
The Sphericity of the Earth
Relative Motion of Sun and Earth
The Seasons
Interpretation of These Observations
Motions and Appearance of the Moon
The Moon's Motion
Phases of the Moon
Lunar Eclipses
Solar Eclipses
Motions of the Planets
The Zodiac
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

3. The Origins of Astronomy

Direction Finding
Megalithic Structures
Astronomical Structures in Asia and the Americas
Timekeeping
Calendars
The Length of the Year
The Lunar Calendar
The Julian Calendar
The Gregorian Calendar
Astronomy and Astrology
The Days of the Week
Early Models of the World
Terms to Know
Ideas to Understand
Simple Observing Projects
Suggestions for Further Reading

4. Early Greek Astronomy

The Idea of an Orderly Universe
Matter as the Basic Reality
Water
Earth, Air, Fire, and Water
Atoms
Mathematics as Basic
Numbers and the Pythagoreans
The Importance of Spheres
Harmony of the Spheres
Geometry as Basic
Uniform Circular Motion
Eudoxus' Model
Aristotle's Cosmological Ideas
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

5. Quantitative Greek Astronomy

The Relative Distances and Sizes of the Sun, Moon, and Earth
The Size of the Earth
The Work of Hipparchus
Precession
The Earth's Motion
Ptolemy the Synthesizer
Distance to the Moon
Ptolemy's System
The Greeks as Scientists
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

6. The Medieval Interlude

The Decline of Astronomy in the West
Islam and Science
Universities Appear
Printing
The Late Medieval World
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

7. The New Astronomy

What Motivated Copernicus?
Aesthetic Reasons
Purifying Ptolemy
The Copernican System
Assumptions
Features of the System
Problems with Copernicus' System
Reception of Copernicus' System
Tycho Brahe
Early Work
Tycho's Planetary Observations
Tycho's Attitude toward Copernicus
Tycho's System
Kepler
Kepler's Attitudes and Motivations
Kepler's Insistence on a Physical Cause
Kepler's Work with Tycho's Data
Kepler's Laws of Planetary Motions
Galileo and the Telescope
Emergence of the Telescope
Galileo's Telescopic Discoveries
The Reception of Galileo's Discoveries
Galileo's Difficulties with the Church
The Old World Starts to Crumble
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

8. The Newtonian Synthesis

Newton's Theory of Motion
The First Law
The Second Law
The Third Law
Why Were Greek Theories of Motion So Different?
The Laws of Motion Applied to Gravity
An Experiment With Falling Objects
Newton's Law of Gravity
A Closer Look at the Law of Gravity
The Force Exerted by the Earth
Your Weight in Space
Newton's Generalizations of Kepler's Laws
Why Kepler's Third Law Works
The Motion of a Satellite in Orbit
Some Aspects of Newton's Laws
Comets
Discovery of Neptune
Beyond the Solar System
Comments on Newton's Laws
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

II: The Life and Death of Stars

9. Radiation and Atoms

Characteristics of Electromagnetic Radiation
Electromagnetic Waves
Wavelength, Amplitude, Speed, and Polarization
The Electromagnetic Spectrum
How the Intensity of Light Falls Off with Distance
Thermal Radiation
The Continuous Spectrum
The Concept of Temperature
Blackbody Radiation
Photons
Wave or Particle?
Atomic Structure and Line Spectra
Constituents of Atoms
What Holds an Atom Together?
The Energy Levels of Atoms
The Spectrum of Hydrogen
Kirchhoff's Laws
The Shell Structure of Atoms
A Few Last Comments
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

10. Telescopes

Optical Telescopes
General Characteristics of Telescopes
Refracting Telescopes
Reflecting Telescopes
A Technique for Coating Glass Mirrors
Large Telescopes
What Do Telescopes Do?
The Effects of the Atmosphere
Radio Telescopes
The Beginnings of Radio Astronomy
Single Dishes
Radio Interferometers
Space Telescopes
Early Work
Orbiting Observatories
Detecting and Analyzing Electromagnetic Radiation
Information Carried by Radiation
Detectors
Instruments
The Doppler Effect
Astrophysics
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

11. Reading Stellar Spectra

Classification of Stellar Spectra
Interpretation of Stellar Spectra
How Absorption and Emission Lines Are Formed
The Hydrogen Balmer Lines
The Temperatures of Stars
Chemical Composition of the Stars
Other Information Provided by Spectra
A Detailed Look at the Surface of an Ordinary Star: The Sun
The Outer Regions of the Sun
Solar Activity
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

12. The Hertzsprung-Russell Diagram

Some Properties of Stars
Stellar Distances
Clusters of Stars
Sizes of Stars
Brightness of Stars
Measuring Distances to Stars
Trigonometric Parallax
The Motions of Stars
The Limits of Trigonometric Parallaxes
Method of Similar Objects
The Hertzsprung-Russell Diagram
Plotting an HR Diagram
Measuring Stellar Masses
Intrinsically Variable Stars
Relative Numbers of Different Kinds of Stars
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

13. Stellar Evolution: Physical Ideas

General Considerations
How Long Do Stars Shine?
Stellar Energy Sources
Understanding the Interior of a Star
The Forces on a Star
Chemical Composition: Opacity
Chemical Composition: Energy Generation
Stellar Models
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

14. The Interstellar Medium: Birthplace of the Stars

Interstellar Clouds
HII Regions
HI Regions
Molecular Clouds
The Intercloud Region
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

15. Stellar Evolution: The Early Phases

Evolution to the Main Sequence
How a Cloud Collapse
Triggering Collapse
Single Stars or Clusters
Evolution of a Protostar When Contraction Stops
Stellar Rotation
The Zero-Age Main Sequence
Main-Sequence Lifetimes
Evolution off the Main Sequence
Massive Stars
Intermediate-Mass Stars
Low-Mass Stars
Interpreting Cluster HR Diagrams
Stellar Populations
Population I Clusters
Population II Clusters
Post-Main-Sequence Evolution of the Sun
Where Are the Sun's Neutrinos?
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

16. Stellar Evolution: The Late Phases

White Dwarfs
General Properties
Observational Evidence
How Stars Become White Dwarfs
Neutron Stars
General Properties
Pulsars: Their Discovery and Characteristics
Pulsars: Energy Generation
Pulsar Spin Rates
How Stars Become Neutron Stars
Black Holes
General Properties
Searching for Black Holes
Candidate Black Holes
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

III: Cosmology: Herschel to the Present

17. The Discovery of Galaxies

Early Ideas of the Nature of Nebulae
Herschel's Work
Telescope Maker and Observer
The Size and Shape of the Milky Way
The Nature of the Nebulae
More Confusion about the Nature of the Nebulae
Discovery of the Spiral Structure
The Distribution of Nebulae
Photographic Evidence
Spectroscopic Results
Further Attempts to Measure Our Galaxy
Star Counts: The Kapteyn Universe
Cepheids as Distance Indicators
Shapley's Method
Hubble Solves the Problem
Final Comments
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

18. The Universe of Galaxies

Types of Galaxies
Spirals
Ellipticals
Irregulars
Peculiar Galaxies
Classification by Content
Classification of the Milky Way
Properties of Galaxies
The Mass of the Milky Way
Finding the Distances to Galaxies
Sizes and Masses of Galaxies
Distributions of Galaxies in Space
Groups and Clusters of Galaxies
Superclusters and Voids
Nonluminous Matter
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

19. The Cosmological Clues

Generalizations about the Universe
Olbers' Paradox
Resolution of Olbers' Paradox
The Cosmological Principle
Are Physical Laws Universally Applicable?
The First Cosmological Clue
Redshifts of Galaxies
Velocity-Distance Relation
What Redshifts Tell Us
The Hubble Constant: How Fast?
The Hubble Constant: For How Long?
The Special Theory of Relativity
The Assumptions of Special Relativity
What We Can All Agree On
Some Consequences of Special Relativity
The Second Cosmological Clue
The 3 K Background Radiation
Its Spectrum
The First Prediction of the Background Radiation
The Third Cosmological Clue
The Origin Helium
Helium and the Density of the Universe
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

20. Violent Events in Galaxies

Radio Galaxies
Thermal and Nonthermal Radio Sources
Quasi-Stellar Objects
Properties of QSOs
Redshifts: Cosmological or Not?
The Nature of QSOs
Matter Between Us and Quasars
Final Comments

21. Models of the Universe

Different Kinds of Geometries
Flat Space
Geometry of Curved Space
Geometry of the Universe
Geometry and Gravity
Test of General Relativity
Observational Tests for the Geometry of the Universe
Origin and Evolution of he Universe
The Big Bang Model
The Steady-State Model
Observational Tests
The Current Picture
Problems with Big Bang Cosmology
The Flatness Problem
The Expansion Age of the Universe
The Horizon Problem
Galaxy Formation Problem
The Matter-Antimatter Problem
Can the Big Bang's Problems Be Solved?
The Fundamental Forces
Unifying the Forces
The Inflationary Universe
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

22. The Evolution of Matter

Changes in the Composition of Mater
Cosmic Abundances
The Evolution of Elements
Changes in the Organization of Matter
Formation of Galaxies
Environmental Effects on Galaxies
The Formation of the Milky Way
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

IV: Worlds Beyond the Earth

23. Planetary Preliminaries

The Space Age and the Solar System
Spaceflight: General Considerations
Spacecraft Instrumentation
Solar-System Properties and Processes
A Quick Look at the Solar System
The Age of the Solar System
The Formation of Planetary Systems
General Properties of Planetary Interiors
Forming Planetary Surfaces
Planetary Atmospheres
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

24. Solar System Planetology

The Terrestrial Planets
The Interior of the Earth
The Earth's Atmosphere
The Moon's Surface
Intercomparison of Terrestrial Objects
The Jovian Planets
General Characteristics
Atmospheres of the Giants
The Interiors of the Giants
Satellites of the Giant Planets
Ring Systems
Pluto
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

25. Life Elsewhere

Life in the Solar System
Early Historical Background
Speculations After Copernicus
The Mars Fad
Compounds Basic to Life
Modern Work
General Biological Requirements for Life
Life Beyond the Solar System
Astronomical Conditions on Parent Stars
Life Elsewhere: Playing with Numbers
Improving the Estimates
More Playing with Numbers: Intelligent Life Elsewhere
Local Circumstances
Searching for Intelligence
Interstellar Travel
Searching for Signals
Which Frequency?
What to Look For?
The Search So Far
A Negative View
Implications of Success or Failure
Terms to Know
Ideas to Understand
Questions
Suggestions for Further Reading

Appendix A

: A Little Arithmetic Scientific Notation
Significant Figures
Order of Magnitude
Angular Measure
Small Angle Formula

Appendix B:

Units of Measurement Mass and Length
Temperature

Appendix C:

How to Simplify Computations

Appendix D:

The Nearest Stars

Appendix E:

The Twenty Brightest Stars

Appendix F:

Planetary Data

Appendix G:

Constellations

Index