Contents

Acknowledgments v"

Introduction 1

The Exploration of the Radio Astronomical Unknown 1

Seeking New Knowledge 2

Radio Astronomy and Imagination 2

1 What is Radio Astronomy? 4

1.1 A Little History 4

1.2 The B irth of Radio Astronomy 5

1.3 So What is Radio Astronomy? 8

1.3.1 How Radio Waves from Space Are Generated 8

1.3.2 Radio Telescopes 8

1.3.3 What is a Radio Source? 10

1.4 Radio Interferometers 11

1.4.1 Very Large Array 11

1.4.2 Very Long Baseline Array 11

2 A Science is Born 14

2.1 Caught between Two Disciplines 14

2.2 Postwar Years-Radar Everywhere 16

2.3 The Southern Skies 18

2.4 Who Could Have Guessed? 19

2.5 Identity Crisis 20

2.6 An Epoch of Discovery 21

3 The Radio Sun and Planets 23

3.1 War Secrets 23

3.2 The Plasma Sun 23

3.3 Solar Radio Emission 25

3.4 The Quiet Sun 25

3.5 Solar Radio Bursts 25

3.6 Radio Signals from the Planets 26

3.7 Jupiter's Radio Bursts 26

3.8 Jupiter's Radiation Belts 27

3.9 The Planets as Radio Sources 29

3.10 Planetary Radar 29

4 The Galactic Radio Nebulae 33

4.1 The Supernova-Stardeath 33

4.2 Recent "Guest Stars" 34

4.3 Cassiopeia A 35

4.4 Supernovae of Type I and Type II - 35

4.5 Supernovae and Life 37

4.6 Emission Nebula-Star Birth 38

4.7 Hll Regions 39

4.8 Planetary Nebulae 39

5 Radio Waves from the Milky Way 40

5.1 "A Steady Hiss Type Static of Unknown Origin" 40

5.2 Receiver Noise—"Listening" to Radio Sources 40

5.3 Grote Reber Maps the Milky Way 42

5.4 A Radio Map of the Whole Sky 42

5.5 The Appearance of the Radio Sky 43

5.6 Polarization of Galactic Radio Waves 44

5.7 "Normal" Galaxies 44

5.8 A Note on Distances - 45

5.9 The Shape of the Milky Way Galaxy 45

5.10 The Center of the Milky Way 46

5.11 Close-Up Radio View of the Galactic Center 47

5.12 The Very Center and the Black Hole 49

6 Interstellar Hydrogen 51

6.1 Clouds of Destiny 51

6.2 Generation of the 21-cm Spectral Line 51

6.3 Observations of Interstellar Neutral Hydrogen 52

6.4 An Image of Interstellar Hydrogen - 52

6.5 Seeing into the Depths of Space 53

6.6 Anomalous Velocity Hydrogen 55

6.7 Interstellar Magnetic Fields 55

6.8 Neutral Hydrogen in Other Galaxies 56

7 Interstellar Molecules 59

7.1 Chemical Factories in Space 59

7.2 What is a Molecule? 62

7.3 Molecular Spectral Lines 62

7.4 Masers in Space 63

7.5 Mega-Masers 66

7.6 Giant Molecular Clouds 66

7.7 The Stages Immediately Following Star Birth 67

8 Pulsars 69

8.1 Scintillation of Radio Sources 69

8.2 The Discovery of Pulsars 69

8.3 Where arc the Pulsars? 71

8.4 Formation of Neutron Stars - 72

8.5 Binary Pulsars—Nature's Fabulous Space Labs 74

8.6 Millisecond Pulsars 76

8.7 What Pulse Timing Tells Us 77

8.8 Pulsars in Globular Clusters 78

9 The Galactic Superstars 79

9.1 The Curious Object SS433 79

9.2 A Black Hole and its Accretion Disk 81

9.3 Precession of the Accretion Disk 82

9.4 Radio Stars 83

9.5 Novae 85

9.6 Other Superstars 86

10 Radio Galaxies 87

10.1 On Finding Distances in Astronomy 87

10.2 Chaos in Distant Galaxies 87

10.3 The Largest "Things" in the Universe 88

10.4 Cygnus A 88

10.5 The Radio Emitting Jets 89

11 Quasars 96

11.1 The Discovery of Quasars 96

11.2 Brightness Variations 97

11.3 Parent Galaxies 98

11.4 Quasars: The Modern View 99

12 The Grand Unification: Active Galactic Nuclei 102

12.1 Cosmic Jets 102

12.2 Seyfert Galaxies 104

12.3 The Energy Diet of a Jet 104

12.4 Faster than Light—Superluminal Motions 105

12.5 Active Galactic Nuclei 106

12.6 Black Holes 107

12.7 Precession 109

12.8 Galactic Cannibalism 110

13 Beyond the Quasars—Radio Cosmology 112

13.1 A Cosmic Perspective 112

13.2 Radio Astronomy and Cosmology 113

13.3 The Microwave Background 114

13.4 Beyond the Big Bang—Multiple Universes 115

13.5 How Smooth is Space? 116

13.6 Missing Mass (Dark Matter?) 118

13.7 Gravitational Lenses 119

14 On the Radio Astronomical Quest for Extraterrestrial

Intelligence 122

14.1 "And Now for Something Completely Different 122

14.2 The Harsh Realities of the SETI Equation—A Modern

Heresy 123

15 Radio Telescopes: The Future 130

15.1 Bigger and Better 131

15.2 Low-Noise Receivers 133

15.3 SMA—The Submillimeter Array 133

15.4 Planned Arrays 133

15.4.1 ALMA 134

15.4.2 LOFAR 136

15.4.3 SKA 137

15.4.4 PAPER 138

16 What's It All About? 140

16.1 Expecting the Unexpected 140

16.2 Are We Still Open to the Unexpected? 141

16.3 How Much Longer Will Radio Astronomy Last? 141

Appendix

A.l "Seeing" Radio Waves 145

A.2 The Electromagnetic Spectrum 145

A.2.1 Wavelength and Frequency 146

A. 2,2 The Wavelength Range of the Electromagnetic

Spectrum 146

A.2.3 Atmospheric Windows 146

A.2,4 Spectral Lines 147

A.2.5 The Redshift and the Doppler Effect 147

A.2.6 Velocities in Radio Astronomy 147

A.3 The Brightness of Radio Sources 148

A.4 Radio Spectra—Identifying the Emission Mechanism 148

A.5 Notation 149

A.6 Position Measurement and Angular Accuracy 149

A.7 Astronomical Coordinate Systems 150

A.8 Astronomical Distances—Looking Back in Time 151

A.9 Keeping Things (Radio) Quiet 151

Index 152

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