John Asher Johnson is professor of astronomy at Harvard University.

One of Choice's Outstanding Academic Titles for 2016 "Johnson's enthusiasm for his vibrant field is palpable in this valuable, concise guide for amateur astronomers and anyone else not afraid of a few technicalities."--Lewis Dartnell, New Scientist "Johnson ... takes us on an enjoyable journey to the world of exoplanet hunters... An excellent book for anyone interested but also for astronomy students if their curriculum includes one?semester course in exoplanets."--Read about Science "This little red book is a thorough yet very understandable introduction to one of the hottest topics in astronomy--planets outside the solar system. Johnson, one of the leading scientists in the field, has created a great primer for undergraduate students wishing to gain enough knowledge to undertake a project or perhaps win an internship in the field."--Choice

• PREFACE ix 1. Introduction 1 1.1 My Brief History 1 1.2 The Human Activity of Watching the Sky 3 1.3 Asking Why the Planets Move as They Do 8 1.4 Exoplanets and Completing the Copernican Revolution 16 2. Stellar Wobbles 23 2.1 At the Telescope 23 2.2 For Every Action 28 2.3 Eccentric Orbits 39 2.4 Measuring Precise Radial Velocities 45 2.5 Stellar Jitter 49 2.6 Design Considerations for a Doppler Survey 52 2.7 Concluding Remarks 57 3. Seeing the Shadows of Planets 59 3.1 Measuring and Reading Transit Signals 62 3.2 The Importance of a/R 71 3.3 Transit Timing Variations 74 3.4 Measuring the Brightness of a Star 77 3.5 Radial Velocities First, Transits Second 81 3.6 Transit First, Radial Velocities Second 83 3.7 From Close In to Further Out 89 4. Planets Bending Space-Time 90 4.1 The Geometry of Microlensing 94 4.2 The Microlensing Light Curve 103 4.3 The Microlensing Signal of a Planet 106 4.4 Microlensing Surveys 109 5. Directly Imaging Planets 114 5.1 The Problem of Angular Resolution 115 5.2 The Problem of Contrast 122 5.3 The Problem of Chance Alignment 129 5.4 Measuring the Properties of an Imaged Planet 130 6. The Future of Planet Hunting 132 6.1 Placing the Solar System in Context 133 6.2 Learning How Planets Form 138 6.3 Finding Life Outside the Solar System 141 6.4 Giant Planets as the Tip of the Iceberg 144 6.5 The Future of the Doppler Method: Moving to Dedicated Instrumentation 148 6.6 The Future of Transit Surveys 153 6.7 The Future of Microlensing 155 6.8 The Future of Direct Imaging 158 6.9 Concluding Remarks 160 BIBLIOGRAPHY 163 GLOSSARY 171 INDEX 177

John Asher Johnson is professor of astronomy at Harvard University.

One of Choice's Outstanding Academic Titles for 2016 "Johnson's enthusiasm for his vibrant field is palpable in this valuable, concise guide for amateur astronomers and anyone else not afraid of a few technicalities."--Lewis Dartnell, New Scientist "Johnson ... takes us on an enjoyable journey to the world of exoplanet hunters... An excellent book for anyone interested but also for astronomy students if their curriculum includes one?semester course in exoplanets."--Read about Science "This little red book is a thorough yet very understandable introduction to one of the hottest topics in astronomy--planets outside the solar system. Johnson, one of the leading scientists in the field, has created a great primer for undergraduate students wishing to gain enough knowledge to undertake a project or perhaps win an internship in the field."--Choice

• PREFACE ix 1. Introduction 1 1.1 My Brief History 1 1.2 The Human Activity of Watching the Sky 3 1.3 Asking Why the Planets Move as They Do 8 1.4 Exoplanets and Completing the Copernican Revolution 16 2. Stellar Wobbles 23 2.1 At the Telescope 23 2.2 For Every Action 28 2.3 Eccentric Orbits 39 2.4 Measuring Precise Radial Velocities 45 2.5 Stellar Jitter 49 2.6 Design Considerations for a Doppler Survey 52 2.7 Concluding Remarks 57 3. Seeing the Shadows of Planets 59 3.1 Measuring and Reading Transit Signals 62 3.2 The Importance of a/R 71 3.3 Transit Timing Variations 74 3.4 Measuring the Brightness of a Star 77 3.5 Radial Velocities First, Transits Second 81 3.6 Transit First, Radial Velocities Second 83 3.7 From Close In to Further Out 89 4. Planets Bending Space-Time 90 4.1 The Geometry of Microlensing 94 4.2 The Microlensing Light Curve 103 4.3 The Microlensing Signal of a Planet 106 4.4 Microlensing Surveys 109 5. Directly Imaging Planets 114 5.1 The Problem of Angular Resolution 115 5.2 The Problem of Contrast 122 5.3 The Problem of Chance Alignment 129 5.4 Measuring the Properties of an Imaged Planet 130 6. The Future of Planet Hunting 132 6.1 Placing the Solar System in Context 133 6.2 Learning How Planets Form 138 6.3 Finding Life Outside the Solar System 141 6.4 Giant Planets as the Tip of the Iceberg 144 6.5 The Future of the Doppler Method: Moving to Dedicated Instrumentation 148 6.6 The Future of Transit Surveys 153 6.7 The Future of Microlensing 155 6.8 The Future of Direct Imaging 158 6.9 Concluding Remarks 160 BIBLIOGRAPHY 163 GLOSSARY 171 INDEX 177