Preface ....................................................... VII
1 Development of the Ideas and Instruments of Modern Solar
Research ..................................................... 1
1.1 Early Telescopic Discoveries on the Sun ................. 1
1.2 The Spectroscope and Photography ........................ 5
1.3 Solar-Terrestial Research and the New Astronomy ......... 8
1.4 Solar Chemical Composition and Energy Generation ....... 14
1.5 The Mt. Wilson Era of Large Telescopes ................. 17
1.6 Advances in Coronal Physics and in the Theory of
Solar Activity ......................................... 22
1.7 Observations at Radio, Ultraviolet, and X-Ray
Wavelengths ............................................ 26
1.8 The Solar Wind and Heliosphere ......................... 28
1.9 Future Directions in Solar Instrumentation ............. 30
2 Radiative Transfer in the Sun's Atmosphere .................. 36
2.1 Photometric Principles ................................. 36
2.1.1 The Radiative Intensity ......................... 36
2.1.2 The Net Outward Flux and the Solar Constant ..... 38
2.2 The Radiative Transfer Equation ........................ 41
2.2.1 The Optical Depth and Source Function ........... 41
2.2.2 Solution for Constant Source Function ........... 43
2.2.3 Solution for a Linear Source Function:
The Eddington-Barbier Relation ......................... 44
2.3 Thermodynamic Equilibrium .............................. 47
2.3.1 The Planck Function ............................. 47
2.3.2 Kirchhoff's Law ................................. 48
2.3.3 Local Thermodynamic Equilibrium (LTE) ........... 49
2.3.4 The Brightness- and Effective Temperatures ...... 50
2.4 The Gray Atmosphere .................................... 50
2.4.1 Formulation of the Problem ...................... 50
2.4.2 Gray Limb Darkening in the Eddington
Approximation ................................... 52
2.4.3 The Photospheric Level Identified with
Radiation at Teff ............................... 53
2.4.4 Radiative Diffusion ............................. 54
2.5 Radiative Transfer in the Fraumhofer Lines ............. 55
2.5.1 Formation of Fraunhofer Lines ................... 55
2.5.2 The Transfer Equation for Lines ................. 56
2.5.3 The Milne-Eddington Model ....................... 57
2.5.4 Comparison with Observations of Line Depth
near Disk Center ................................ 58
2.5.5 Comparison with Observed Center-to-Limb
Behavior ........................................ 60
3 Solar Spectroscopy .......................................... 65
3.1 A Survey of the Sun's Spectrum ......................... 65
3.2 Atomic Structure ....................................... 74
3.3 Space Quantization and the Zeeman and Stark Effects .... 78
3.3.1 The Zeeman Effect ............................... 79
3.3.2 The Stark Effect ................................ 84
3.4 Multiplet Rules for Transitions ........................ 86
3.5 Atomic Transitions and their Excitation ................ 88
3.6 Rates for Radiative Transitions ........................ 90
3.7 Boltzmann Equilibrium and the Saha Equation ............ 91
3.8 Rate Equations in Statistical Equilibrium .............. 93
3.9 Line Broadening ........................................ 95
3.9.1 Thermal and Turbulent Doppler Broadening ........ 95
3.9.2 Radiation Damping and Pressure Broadening ....... 97
3.9.3 Broadening by Self-Absorption ................... 98
3.9.4 Analysis of the Observed Profile of
a Spectral Line ................................. 98
3.10 Molecules on the Sun .................................. 100
4 Dynamics of Solar Plasmas .................................. 103
4.1 Hydrostatic Equilibrium ............................... 104
4.1.1 Equilibrium in a Homogeneous Gravitational
Field .......................................... 104
4.1.2 Self-Gravitating Atmospheres ................... 105
4.1.3 The Polytropic Approximation ................... 105
4.2 The Equations of Motion ............................... 207
4.2.1 Euler's Equation ............................... 107
4.2.2 Viscous Forces and the Navier-Stokes
Equation ....................................... 108
4.2.3 The Equation of Continuity ..................... 110
4.2.4 The Heat-Balance Equation ...................... 111
4.2.5 Conservation of Total Energy ................... 114
4.3 The Influence of Magnetic Fields in Solar Plasma
Dynamics .............................................. 115
4.3.1 The Lorentz Force .............................. 115
4.3.2 The Importance of Self-induction ............... 116
4.3.3 The Diffusive and "Frozen-in"
Approximations ................................. 117
4.4 Wave Motions in the Sun ............................... 119
4.4.1 Types of Waves Expected and Observed ........... 119
4.4.2 Soundwaves ..................................... 119
4.4.3 Simple Waves and Shock Formation ............... 120
4.4.4 Properties of Shock Waves ...................... 121
4.4.5 Magnetohydrodynamic Waves ...................... 123
4.4.6 Internal Gravity Waves ......................... 125
4.4.7 Plasma Oscillations ............................ 125
4.5 Charged Particle Dynamics ............................. 126
4.5.1 Validity of the Continuum Approximation and
of Thermal Equilibrium ......................... 126
4.5.2 Charged Particle Motions ....................... 127
5 The Photosphere ............................................ 133
5.1 Observations of the Quiet Photosphere ................. 135
5.1.1 Limb Darkening ................................. 135
5.1.2 Observed Properties of Granulation ............. 138
5.1.3 The Supergranulation and Photospheric
Network ........................................ 143
5.2 Construction of a Photospheric Model .................. 146
5.2.1 Physical Assumptions ........................... 146
5.2.2 Determination of the Temperature Profile
from Continuum Limb Darkening .................. 147
5.3 Determination of the Photospheric Opacity ............. 148
5.3.1 The Empirical Technique ........................ 148
5.3.2 The Sources of Photospheric Opacity ............ 149
5.4 Physical Structure and Energy Balance of the
Photosphere ........................................... 150
5.4.1 Models of Photospheric Structure ............... 150
5.4.2 Comparison with Observations ................... 153
5.4.3 Energy Transport Mechanisms in the
Photosphere .................................... 155
5.5 The Photospheric Chemical Composition and the
Curve of Growth ....................................... 156
5.5.1 The Theoretical Curve of Growth ................ 157
5.5.2 Comparison with the Empirical Curve ............ 160
5.6 The Sun's Chemical Composition ........................ 162
6 The Sun's Internal Structure and Energy Generation ......... 167
6.1 Equations of Stellar Structure ........................ 168
6.1.1 Mechanical Equilibrium ......................... 168
6.1.2 Energy Transport ............................... 169
6.1.3 Boundary Conditions ............................ 170
6.2 Physical Parameters Required for the Solution ......... 171
6.2.1 Chemical Composition ........................... 171
6.2.2 The Mean Molecular Weight ...................... 172
6.2.3 The Ratio of Specific Heats .................... 172
6.2.4 The Radiative Opacity .......................... 173
6.2.5 Energy Generation Processes .................... 174
6.3 Nuclear Reactions in the Sun's Interior ............... 174
6.3.1 Factors That Determine the Dominant
Reactions ...................................... 174
6.3.2 The Proton-Proton Chain ........................ 175
6.3.3 The Carbon-Nitrogen Cycle ...................... 177
6.3.4 Nuclear Energy Generation Rates ................ 179
6.4 The Standard Model of Physical Conditions in the
Solar Interior ........................................ 180
6.5 Observational Tests of the Standard Model ............. 183
6.5.1 Solar Neutrino Observations .................... 183
6.5.2 Lithium and Beryllium Abundances ............... 186
6.5.3 Stellar Structure and Evolution ................ 187
6.5.4 Geological and Climatological Evidence ......... 189
6.5.5 The Sun's Angular Momentum and Shape ........... 190
6.5.6 Solar Oscillations ............................. 191
7 Rotation, Convection, and Oscillations in the Sun .......... 195
7.1 Observations of Solar Rotation ........................ 196
7.1.1 Photospheric Doppler Measurements .............. 196
7.1.2 Helioseismic Measurements of Rotation in the
Solar Interior ................................. 198
7.1.3 Tracer Measurements ............................ 199
7.2 Measurements on Convection ............................ 201
7.2.1 Observations of Convection at the
Photosphere .................................... 201
7.2.2 Comparison with Laboratory Measurements ........ 202
7.3 Dynamics of Solar Convection and Rotation ............. 203
7.3.1 Condition for Onset of Convection .............. 203
7.3.2 Gravity Waves .................................. 205
7.3.3 Mixing Length Theory ........................... 206
7.3.4 Dynamics of Convection in a Plane Layer ........ 208
7.3.5 Models of Granulation .......................... 209
7.3.6 Dynamics of Supergranulation ................... 212
7.3.7 Dynamics of the Solar Interior ................. 212
7.4 Observations of Solar Oscillations .................... 215
7.4.1 The 5-min Oscillations ......................... 215
7.4.2 Oscillations of Longer and Shorter Periods ..... 219
7.5 Interpretation of Solar Oscillations .................. 220
7.5.1 Resonances in the Sun .......................... 220
7.5.2 Oscillation Modes of the Solar Interior ........ 223
7.5.3 Excitation and Damping Mechanisms .............. 225
7.5.4 Comparison of the Observed and Calculated
Properties of the p-Modes ...................... 226
7.5.5 Oscillations as a Probe of the Solar
Interior ....................................... 228
8 Observations of Photospheric Activity and Magnetism ........ 233
8.1 Sunspot Observations .................................. 234
8.1.1 Structure of the Umbra and Penumbra ............ 234
8.1.2 Birth and Evolution of Spot Groups ............. 240
8.1.3 Photometry and Spectra of Umbrae ............... 241
8.1.4 Mass Motions and Oscillations .................. 244
8.2 Dynamics of Spots ..................................... 247
8.2.1 Thermal Structure of the Umbra ................. 247
8.2.2 Why Spots Are Cool ............................. 249
8.2.3 Why Spots Cause Dips in the Solar
Luminosity ..................................... 251
8.2.4 Dynamics of Sunspot Evolution .................. 252
8.3 Faculae ............................................... 254
8.3.1 Structure and Evolution ........................ 254
8.3.2 Physical Measurements .......................... 254
8.3.3 Why Faculae Are Bright ......................... 259
8.4 Observations of Solar Magnetism ....................... 261
8.4.1 The Sunspot Magnetic Field ..................... 261
8.4.2 Photospheric Fields in Faculae and Magnetic
Network ........................................ 263
8.4.3 Large-Scale Structure and Evolution of the
Photospheric Field ............................. 266
8.4.4 Global Structure of the Sun's Magnetic
Field .......................................... 272
9 The Chromosphere and Corona ................................ 277
9.1 The Chromosphere ...................................... 278
9.1.1 Observations of Structures and Motions at
the Limb ....................................... 278
9.1.2 Observations on the Disk ....................... 281
9.1.3 Physical Conditions ............................ 288
9.1.4 Energy Balance ................................. 293
9.1.5 Chromospheric Heating .......................... 293
9.1.6 Dynamics of Spicules and Fibrils ............... 295
9.2 The Corona and Transition Region ...................... 297
9.2.1 Spectrum and Radiation Mechanisms .............. 297
9.2.2 Structures of the Corona and Transition
Region ......................................... 298
9.2.3 Magnetic Fields and Plasma Motions ............. 303
9.2.4 Physical Conditions in Closed and Open
Magnetic Structures ............................ 306
9.2.5 Heating and Dynamics of Coronal Loops and
Holes .......................................... 311
10 Prominences and Flares ..................................... 319
10.1 Prominences and Filaments ............................. 320
10.1.1 Observations and Physical Conditions .......... 320
10.1.2 Dynamics ...................................... 324
10.2 Flares ................................................ 331
10.2.1 Observations and Physical Conditions .......... 331
10.2.2 Energy Release and Dynamics ................... 344
10.2.3 Acceleration of Energetic Charged
Particles ..................................... 348
11 Dynamics of the Solar Magnetic Field ....................... 351
11.1 Dynamics of Solar Magnetic Flux Tubes ................. 351
11.1.1 Dynamical Equilibrium and Geometry ............. 351
11.1.2 Dynamical Stability ............................ 355
11.1.3 Thermal Instability ............................ 357
11.1.4 Steady Flows ................................... 358
11.1.5 Oscillations and Waves ......................... 360
11.1.6 Magnetic Field Dissipation ..................... 363
11.2 Activity Behavior over the Solar Cycle ................ 365
11.2.1 The Sunspot Number and Other Activity
Indices ........................................ 365
11.2.2 Time Behavior of the Sun's Magnetic Field ...... 367
11.2.4 Long-Term Behavior of Solar Activity ........... 371
11.3 Dynamics of the Solar Magnetic Cycle .................. 376
11.3.1 The Babcock Model of the Solar Cycle ........... 376
11.3.2 Dynamical Dynamo Models ........................ 379
12 The Solar Wind and Heliosphere ............................. 387
12.1 Structure of the Solar Wind ........................... 388
12.1.1 In Situ Measurements of Particles and
Fields ......................................... 388
12.1.2 Observations Out of the Ecliptic Plane ......... 393
12.1.3 Cosmic Rays .................................... 394
12.1.4 Interplanetary Gas and Dust .................... 398
12.1.5 Structure of the Heliosphere ................... 400
12.2 Transient Features in the Solar Wind .................. 402
12.2.1 High-Speed Streams ............................. 402
12.2.2 Interplanetary Shock Waves ..................... 403
12.2.3 Coronal Mass Ejections (CME's) ................. 405
12.3 Dynamics of the Solar Wind ............................ 407
12.3.1 Thermal Conductivity of the Corona ............. 407
12.3.2 Expansion of the Corona ........................ 408
12.3.3 Geometry of the Interplanetary Magnetic
Field .......................................... 411
12.3.4 Energy and Angular Momentum Fluxes ............. 412
12.3.5 Sources of the Wind ............................ 415
13 The Sun, Our Variable Star ................................. 421
13.1 The Sun Compared to other Stars ....................... 422
13.1.1 The Sun's Location and Proper Motion in
the Galaxy ..................................... 422
13.1.2 Mass, Chemical Composition and Spectrum ........ 423
13.1.3 Luminosity, Radius, and Effective
Temperature .................................... 424
13.1.4 Chromospheric and Coronal Radiations ........... 425
13.1.5 Stellar Winds and Mass Loss .................... 426
13.1.6 Angular Momentum and Magnetism ................. 426
13.2 Evolution of the Sun .................................. 427
13.2.1 The H-R Diagram and Stellar Evolution .......... 427
13.2.2 The Sun's Future Evolution ..................... 431
13.2.3 The Early Sun .................................. 433
13.3 Solar and Stellar Variability ......................... 438
13.3.1 Observations of Stellar Activity ............... 438
13.3.2 Mechanisms of Stellar Activity ................. 442
13.3.3 The Sun's Variable Outputs ..................... 446
13.3.4 Prediction of Solar Activity and Space
Weather ........................................ 453
Index ......................................................... 459
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