| Physics 015: The Course Notes, Fall 2004
An important remark: the course notes are divided into sections and subsections, with titles as shown below. Please note that the division is meant to be logical, by topic. You should not necessarily assume that that one section of notes corresponds to exactly one lecture! The important thing is to read them sequentially, and to refer to the
suggested readings in the textbook and elsewhere which are intended to parallel these discussions.
Contents:1. Opening Remarks: Setting the Scene 1 Varied Perspectives 2 Remarks on Mathematics 3 The Great Discoveries in 20th Century Science 4 We Live at a Special Time 5 Your Astronomical Awareness 2. The Science of Astronomy 1 Why Should We Be Interested in Astronomy at All? 2 Astronomy as a Science 3 The Unimportance of Large Numbers 4 Getting Used to Large Numbers 3. The Importance of Scale: A First Conservation Law 1 Scales Influence Perception 2 Scales Determine Form and Function 3 The Relevance of External Gravity 4 The Importance of Proportions 5 Self-Gravity Can Determine Form 6 Self-Gravity Determines Temperature: A First Conservation Law 7 Putting It All Together 4. The Dominance of Gravity 1 Why is Gravity Dominant? The Story of Four Forces 5. Looking Up 1 A Musical Interlude 2 How Does Information Reach Us from the Universe? 3 Prominent Phenomena Making Regular Appearances 4 Vestiges From the Past 5 More Regularities 6 What Conclusions Might the Ancients Have Drawn? 7 What Would You Like to Know? 6. The Seasons 1 Welcome Fall! 2 The Sun's Motion Differs from That of the Stars 3 The Orientation of the Earth -- An Introduction to 'Limiting Cases' 7. The Spin of the Earth: Another Conservation Law 1 Another Example of a Conservation Law: Angular Momentum 2 Why the Stability? 3 Matters of Definition: Rotation and Revolution 8. The Earth: Shape, Size, and State of Rotation 1 The Shape of the Earth 2 The Size of the Earth 3 Degrees of Correctness 4 The Rotation of the Earth 9. The Moon: Shape, Size, Nature 1 The Apparent Size of the Moon 2 The Cause of the Lunar Phases 3 Eclipses of Two Kinds 4 The Size of the Moon 5 The Distance of the Moon 6 The Flatness of the Sky: Depth Perception and the 'Travelling Moon' 10. The Relative Distances and Sizes of the Sun and Moon 1 First Indications 2 The Argument of Aristarchus 11. Further Considerations: Planets and Stars 1 The Relative Distances of the Planets 2 The Relative Distances of the Sun and Stars 3 The Composition and Nature of the Stars and Planets 4 Where Do We Stand Now? Keeping Things in Perspective 12. The Moving Earth 1 Welcome to the Dance 2 Does the Earth Actually Move Through Space? 13. Stellar Parallax: The Astronomical Chicken 1 Distances from Stellar Parallaxes 2 The Astronomical Chicken 14. Greek Cosmology 1 Reasons to Consider a Heliocentric Model 2 The Fundamental Postulates of Greek Cosmology 3 Problems with the Greek Cosmology 4 The Ptolemaic Model: Problems Fixed(?) 5 Did the Greeks Seriously Believe this Model? Occam's Razor 6 Could the Ptolemaic Model Have Been Tested? 7 In Defence of the Ancients: Reasons to Consider a Geocentric Model 15. Stonehenge 1 Some Myths Dispelled 2 The Astronomical Significance 16. The Pyramids 1 Science or Non-Science? 2 Astronomical Alignments in the Pyramids 3 The Pole Star: Precession 17. Copernicus Suggests a Heliocentric Cosmology 1 The Historical Context 2 Meet the Principal Players 3 Copernicus Provides the Idea 18. Tycho Brahe, the Master Observer 1 A Difficult Man 2 Two Important Discoveries 3 Tycho's Revolutionary Philosophy 4 Tycho's Own 'World Model' 19. Kepler the Mystic 1 Laws in Threes 2 A Philosophical Starting Point, and a Bold Assumption 3 Some Simple Surveying 4 Just a Scale Model 5 The Obvious Questions, and Three Laws 6 K-I: The Shapes of the Orbits 7 K-II: No Planet Moves at Constant Speed 8 K-III: No Two Planets Move at the Same Speed 9 Kepler the Mystic 20. Galileo Provides the Proof 1 Galileo the Experimenter 2 The Concept of Relativity 3 Galileo's Need for a Telescope: The Inadequacy of the Human Eye 4 How a Telescope Works 5 Galileo's Principal Astronomical Discoveries: The First Four 6 The Significance of These Four Observations 7 Two Critical Astronomical Discoveries 8 The Significance of Galileo's Observations of Jupiter and Venus 9 The End of the Galileo Story 10 Where Are We Now? The Need for Some Real Physics 21. Light: Introductory Remarks 1 Studying the Past 2 Obvious Questions and Historical Musings 3 The Speed of Light - and That of Sound 4 Roemer's Studies of Jupiter: Timekeeping and Navigation 22. Light as a Wave 1 Wave Phenomena in General 2 Diffraction: Waves Spreading Out from a Hole 3 Diffraction: Waves 'Bending' Around Corners 4 Interference: Waves Interacting with One Another 5 Polarization: More Evidence for Waves 6 Waves in What? 7 Electromagnetic Waves 23. Light as Particles 1 The Photoelectric Effect: An Analogy 2 The Photoelectric Effect: The Reality 3 The Wave-Particle Duality 24. The Full Spectrum of Light 1 An Introduction to the Electromagnetic Spectrum 2 How Does a Prism Work? Refraction 3 How Does a Prism Work? Dispersion 4 An Important Technical Point 5 Reflected Versus Emitted Light 6 Why Do Only Some Objects Emit Light? 7 The Entire Spectrum 8 What Can We See? 9 Light Carries Energy and Momentum 25. Interpreting the Emitted Light 1 The Effects of Distance on Brightness 2 Thermal Radiators (Perfect Radiators, or Blackbodies) 3 A Logical First Guess 4 The Distribution of Radiated Energy: Shape, Total, and Peak 5 Shape: The Planck Law 6 A Digression: Measuring Temperatures in Kelvins 7 Total: Stefan's Law 8 The Importance of Size: A Specific Case, and a Warning 9 Peak: The Wien Displacement Law 10 When Temperature Isn't a Factor 26. Kirchhoff's Laws and Stellar Spectra 1 Kirchhoff's Three Laws: The Parable of the Piano Players 2 The Parable in Light 3 Spectral Signatures 4 The Spectrum of the Sun: The Solar Atmosphere 5 The Composition of the Stars: Within Our Grasp? 6 The Composition of the Sun; Helium 7 Spectral Classification 8 More From Stellar Spectra 9 An Important Warning 27. Understanding Kirchhoff's Laws 1 The Parable Explained: Electrons in Orbits 2 A Simple Visualisation 3 One Important Difference: No Well-Defined Orbits 4 And One Critical Difference: Quantized Orbits 5 Why Quantized? 6 A Homespun Analogy 7 The Inevitability and Promptness of the Fall 8 A Diversity of Paths 9 The Spacing of the Shelves 10 Kirchhoff's Second Law: Why Diffuse Gases Produce Emission Lines 11 Ionization 12 Kirchhoff's Third Law: The Formation of Absorption Lines 13 Why Are There Sources of Continuous Radiation at All? 28. The Doppler Effect 1 An Introduction 2 The Luggage Carousel as a 'Wave Generator' 3 Speeding Up a Slow Process: Raise the Apparent Frequency 4 Give Yourself Time to Think: Lower the Apparent Frequency 5 Consider a Moving Source 6 Drawing Interesting Inferences 7 The Physics of the Source: An Application to Light 8 Consider a Surfer 9 Some History: The Doppler Effect in Sound 10 A Modern Example 11 The Question of Speed: The Perplexing Behaviour of Light 12 Light and the Doppler Shift: An Everyday Example 13 The Colours and Velocities of the Stars 29. Astronomical Telescopes 1 The Earliest Telescopes 2 The Role of the Eyepiece - and Its Irrelevance 3 Why Make Big Telescopes? 4 How Telescopes are Used 5 The Problem with Refractors 6 The Advent of Reflecting Telescopes 7 Solving the Problems Posed by Refractors 8 Varied Designs of Reflectors 9 Innovations in Optical Astronomy 10 The Theoretical Resolution Limits 30. The Great Observatories 1 Welcome to Hawaii 2 Creating an Observatory: Funding a Telescope 3 Is It Worth All the Money? 4 Where to Put a Telescope 5 Observing at Mauna Kea 6 A Prosaic Question: Why Glass Mirrors? 7 Making the Glass Shiny 31. Making the Most of Optical Astronomy 1 The Need to Go Faint 2 Accomplishing This Worthwhile Goal 3 Moving From Inefficient to Efficient Detectors 4 The Problem with CCDs 5 Multiplexed Observing - But First a Digression 6 Globular Star Clusters in the Milky Way 7 Globular Star Clusters in Other Galaxies 8 The Practical Challenges 9 The Problems Solved: Multiplexed Observations 32. Adaptive Optics: Beating the Sky 1 Reduce the Background 2 Make the Sharpest Images Possible 3 Controlling the Sheep 4 Our Sheepdog: A Rubber Mirror 5 Feedback 6 Astronomical Feedback: Studying the Image 7 Turn on the Lasers! 8 The Results 33. Radio Astronomy 1 The Early Days 2 Modern Considerations 3 Arecibo 4 The Very Large Array 5 Interferometry 6 Making Our Interferometers Bigger 7 Why Bother? An Important Reminder 34. Observing at Other Wavelengths 1 The Importance of the Atmosphere 2 Satellite Astronomy: Looking Down 3 Infrared 4 Ultraviolet 5 X-Rays 6 Serendipity in Astronomy: The Discovery of X-Rays 7 Gamma Rays: More Serendipity 8 Skipping Stones 9 The Interesting Physics of Water 10 The Trouble with Hubble 35. Isaac Newton's Physics 1 Meet Isaac Newton 2 The First Law: Inertia Formalised 3 The Second Law: When Forces Are Unbalanced 4 The Third Law: Action and Reaction 5 Deterministic Physics 6 The Great Conservation Laws 7 How Rockets Work 8 What is Missing? 36. Newtonian Gravity Explains It All 1 Action at a Distance 2 Testing the Law 3 Gravity: A Modern Perspective 4 Calculus, and a Remarkable Simplification 5 Digression: A First Thought About Black Holes 6 Point Masses 7 Ballistic Motions 8 Kepler Explained - And Expanded! 9 Conic Sections 10 Kepler's Second Law Revisited 11 Dumbbells in Space 12 Escaping from a Planet: Rockets 13 Escaping from a Planet: Gases 37. Weight 1 How Much Do You Weigh? A Thought Experiment 2 Space Stations 3 A Remarkable Coincidence? 4 The Principle of Equivalence 5 Determining Masses in Astronomy: What Not to Do 6 'Weighing' the Earth 7 The Masses of the Other Planets and the Sun 8 The Last Frontier: Weighing the Stars 38. The Success of Newtonian Gravity 1 The Discovery of Uranus 2 The Prediction and Discovery of Neptune: A Real Success 3 Halley and the Comet 4 The Prediction and Discovery of Pluto: An Apparent Success 5 Serendipity in Astronomy: The Story of Pluto's Moon 6 Using Gravity in Studying Pluto: A Reconsideration of Its Discovery 39. The Ultimate Failure of Newtonian Gravity 1 The Strange Behaviour of Mercury 2 The Futile Search for Vulcan 3 Einstein Provides the Answer 4 Another Prediction: The Bending of Light 5 The Prediction Confirmed... 6 ...and Also on Larger Scales 7 The Limitations of Newtonian Gravity 40. Tsunamis and Tides 1 Tsunamis 2 What Are Tides? 3 When Might Tides Matter? 4 The Ocean Tides of the Earth 5 The Influence of the Sun 6 Complications and Consequences 41. The Organization of the Solar System 1 What Would We Like To Know? 2 A Messy Complication 3 Three Possible Origins 4 Obvious Regularities 42. Solar System Formation 1 Haphazard Accumulation? No! 2 A Catastrophic Origin? 3 A Profound Implication: Our Uniqueness 4 The Nebular Hypothesis 5 What Starts the Collapse? 6 Cloud Flattening 7 Condensation Mechanisms 8 After the Pebbles: Planetesimals and Protoplanets 9 Where Does the Leftover Gas Go? The Magic Broom 10 Some Final Predictions 11 Other Solar Systems? 43. The Age of the Solar System 1 Introductory Remarks: Guessing Ages 2 Thinking About Cows 3 An Introduction to Atoms 4 Isotopes 5 Heavy Water 6 Isotopes of Many Kinds? 7 Instabilities and Transmutations: The Alchemist's Dream 8 Alpha, Beta, Gamma: Three Kinds of Decay 9 Decays in Series 10 Decays and Death Rates 11 Constructing a Clock 12 What Ages Anyway? 13 What Chronometers Do We Use? 14 Other Applications: Medicine, and Carbon Dating 44. Planetary Structure: The Earth 1 The Challenge of Remote Sensing 2 A Medical Analogy 3 The Interior of the Earth: Varied Approaches 4 Ultrasonics and Seismology 5 The Earth's Active Geology 45. Solar System Leftovers 1 The Nature of Comets 2 Meteors: Some Basic Definitions 3 Meteor Showers 4 Asteroids 5 Meteorites: The Collected Debris 6 Meteorites: The Geological Record 7 Tunguska: A Recent Example 46. The Vulnerability of the Earth 1 Lessons For Us All 2 From Catastrophism to Gradualism - and Back Again 3 Comet Shoemaker-Levy 4 Recent Comet Extravaganzas 5 The Big One: The Extinction of the Dinosaurs 6 Did It Really Happen? If So, Where? 7 The Statistics 8 What Can We Do About It? 47. Venus 1 A Study in Contradictions 2 The Appearance of Venus: Its Importance 3 Transits of Venus: Captain Cook 4 The Rotation of Venus: Cook That Chicken 5 The Surface of Venus 6 An Introduction to the Greenhouse Effect 7 The Structure of Atmospheres 8 Other Warm Parts of the Atmosphere 9 The Meaning of Temperature 10 Consider a Fireplace 11 Back to Venus... 12 ...and Back to the Earth 13 The Critical Point 14 In Your Own Home 15 Some Everyday Examples 16 The Fundamental Cause of Venus's Greenhouse Effect 17 A Warning for the Earth 48. Mars 1 Welcome to Mars 2 Historical Perspectives 3 The Legacy of Percival Lowell 4 War of the Worlds: Moral Questions 5 Early Flybys of Mars 6 The Orbiters and the Martian Moons 7 The Martian Surface Unveiled: The First Discoveries 8 The Viking Landers 49. The Search for Martian Life 1 LAWKI 2 Primitive or Advanced Life Forms? 3 Evidence of Absence 4 How to Search 5 The First Test: Have a Look Around 6 The Second Test: Find the Body 7 Tests Three Through Five: Look for Metabolic Activity 8 And the Results... 9 The Present Interpretation 10 Other Prospects for Present Life on Mars 11 Where Did All the Water Go? 12 Will the Water Flow Again? 13 Fossilised Martian Life Forms? 14 Back We Go... Next chapter
0: Physics 015: The Course Notes, Fall 2004 1: Opening Remarks: Setting the Scene. 2: The Science of Astronomy: 3: The Importance of Scale: A First Conservation Law. 4: The Dominance of Gravity. 5: Looking Up: 6: The Seasons: 7: The Spin of the Earth: Another Conservation Law. 8: The Earth: Shape, Size, and State of Rotation. 9: The Moon: Shape, Size, Nature. 10: The Relative Distances and Sizes of the Sun and Moon: 11: Further Considerations: Planets and Stars. 12: The Moving Earth: 13: Stellar Parallax: The Astronomical Chicken 14: Greek Cosmology: 15: Stonehenge: 16: The Pyramids: 17: Copernicus Suggests a Heliocentric Cosmology: 18: Tycho Brahe, the Master Observer: 19: Kepler the Mystic. 20: Galileo Provides the Proof: 21: Light: Introductory Remarks. 22: Light as a Wave: 23: Light as Particles. 24: Full Spectrum of Light: 25: Interpreting the Emitted Light: 26: Kirchhoff's Laws and Stellar Spectra. 27: Understanding Kirchhoff's Laws. 28: The Doppler Effect: 29: Astronomical Telescopes: 30: The Great Observatories: 31: Making the Most of Optical Astronomy: 32: Adaptive Optics: Beating the Sky. 33: Radio Astronomy: 34: Observing at Other Wavelengths: 35: Isaac Newton's Physics: 36: Newtonian Gravity Explains It All: 37: Weight: 38: The Success of Newtonian Gravity: 39: The Ultimate Failure of Newtonian Gravity: 40: Tsunamis and Tides: 41: The Organization of the Solar System: 42: Solar System Formation: 43: The Age of the Solar System: 44: Planetary Structure: The Earth. 45: Solar System Leftovers: 46: The Vulnerability of the Earth: 47: Venus: 48: Mars: 49: The Search for Martian Life: 50: Physics 015 - Parallel Readings.
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(Wednesday, 21 April, 2021.)