ESSENTIAL PHYSICS
CONTENTS 1 OBSERVING THE UNIVERSE 1 1 1 WHAT DO ASTRONOMERS AND ASTROPHYSICISTS DO 1 1 2 OUR PLACE ON EARTH 2 1 3 LOCATION IN THE SKY 4 1 4 MEASURING ANGLE AND SIZE 9 1 5 THE LOCATIONS OF THE STARS ARE SLOWLY CHANGING 10 1 6 WHAT TIME IS IT 15 1 7 TELLING TIME BY THE STARS 17 1 8 OPTICAL TELESCOPES OBSERVE VISIBLE LIGHT 19 1 9 TELESCOPES THAT DETECT INVISIBLE RADIATION 23 1 10 UNITS USED BY ASTRONOMERS AND ASTROPHYSICISTS 27 1 11 PHYSICAL CONSTANTS 30 2 RADIATION 33 2 1 ELECTROMAGNETIC WAVES 33 2 2 THE ELECTROMAGNETIC SPECTRUM 37 2 3 MOVING PERSPECTIVES 40 2 4 THERMAL BLACKBODY RADIATION 44 2 5 HOW FAR AWAY IS THE SUN AND HOW BRIGHT BIG AND HOT IS IT 50 2 5 1 DISTANCE OF THE SUN 50 2 5 2 HOW BIG IS THE SUN 54 2 5 3 THE UNIT OF ENERGY 54 2 5 4 THE SUN S LUMINOSITY 55 2 5 5 TAKING THE SUN S TEMPERATURE 55 2 5 6 HOW HOT ARE THE PLANETS 56 2 6 THE ENERGY OF LIGHT 59 2 7 RADIATION SCATTERING AND TRANSFER 61 2 7 1 WHY IS THE SKY BLUE AND THE SUNSETS RED 61 2 7 2 RAYLEIGH SCATTERING 62 2 7 3 THOMSON AND COMPTON SCATTERING 63 2 7 4 RADIATION TRANSFER 65 3 GRAVITY 69 3 1 CEASELESS REPETITIVE PATHS ACROSS THE SKY 69 3 2 UNIVERSAL GRAVITATIONAL ATTRACTION 73 3 3 MASS OF THE SUN 80 3 4 TIDAL EFFECTS 81 3 4 1 THE OCEAN TIDES 81 3 4 2 TIDAL LOCKING INTO SYNCHRONOUS ROTATION 85 3 4 3 THE DAYS ARE GETTING LONGER 85 3 4 4 THE MOON IS MOVING AWAY FROM THE EARTH 87 3 4 5 A PLANET S DIFFERENTIAL GRAVITATIONAL ATTRACTION ACCOUNTS FOR PLANETARY RINGS 90 3 5 WHAT CAUSES GRAVITY 93 4 COSMIC MOTION 99 4 1 MOTION OPPOSES GRAVITY 99 4 1 1 EVERYTHING MOVES 99 4 1 2 ESCAPE SPEED 99 4 2 ORBITAL MOTION 101 4 3 THE MOVING STARS 105 4 3 1 ARE THE STARS MOVING 105 4 3 2 COMPONENTS OF STELLAR VELOCITY 105 4 3 3 PROPER MOTION 107 4 3 4 RADIAL VELOCITY 107 4 3 5 OBSERVED PROPER MOTIONS OF STARS 109 4 3 6 MOTIONS IN STAR CLUSTERS 111 4 3 7 RUNAWAY STARS 114 4 4 COSMIC ROTATION 116 4 4 1 UNEXPECTED PLANETARY ROTATION 116 4 4 2 THE SUN S DIFFERENTIAL ROTATION 120 4 4 3 STELLAR ROTATION AND AGE 124 5 MOVING PARTICLES 125 5 1 ELEMENTARY CONSTITUENTS OF MATTER 125 5 2 HEAT TEMPERATURE AND SPEED 130 5 2 1 WHERE DOES HEAT COME FROM 130 5 2 2 THERMAL VELOCITY 132 5 2 3 COLLISIONS 134 5 2 4 THE DISTRIBUTION OF SPEEDS 135 5 3 MOLECULES IN PLANETARY ATMOSPHERES 138 5 4 GAS PRESSURE 141 5 4 1 WHAT KEEPS OUR ATMOSPHERE UP 141 5 4 2 THE IDEAL GAS LAW 142 5 4 3 THE EARTH S SUN LAYERED ATMOSPHERE 144 5 4 4 PRESSURE TEMPERATURE AND DENSITY INSIDE THE SUN 148 5 5 PLASMA 149 5 5 1 IONIZED GAS 149 5 5 2 PLASMA OSCILLATIONS AND THE PLASMA FREQUENCY 152 5 5 3 ATOMS ARE TORN APART INTO PLASMA WITHIN THE SUN 153 5 6 SOUND WAVES AND MAGNETIC WAVES 154 5 6 1 SOUND WAVES 154 5 6 2 MAGNETIC WAVES 156 6 DETECTING ATOMS IN STARS 159 6 1 WHAT IS THE SUN MADE OUT OF 159 6 2 QUANTIZATION OF ATOMIC SYSTEMS 165 6 3 SOME ATOMS ARE EXCITED OUT OF THEIR LOWEST ENERGY GROUND STATE 173 6 4 IONIZATION AND ELEMENT ABUNDANCE IN THE SUN AND OTHER STARS 176 6 5 WAVELENGTHS AND SHAPES OF SPECTRAL LINES 180 6 5 1 RADIAL MOTION PRODUCES A WAVELENGTH SHIFT 180 6 5 2 GRAVITATIONAL REDSHIFT 181 6 5 3 THERMAL MOTION BROADENS SPECTRAL LINES 183 6 5 4 ROTATION OR EXPANSION OF THE RADIATING SOURCE CAN BROADEN SPECTRAL LINES 184 6 5 5 CURVE OF GROWTH 185 6 5 6 MAGNETIC FIELDS SPLIT SPECTRAL LINES 186 7 TRANSMUTATION OF THE ELEMENTS 191 7 1 THE ELECTRON X RAYS AND RADIUM 191 7 2 RADIOACTIVITY 193 7 3 TUNNELING OUT OF THE ATOMIC NUCLEUS 196 7 4 THE ELECTRON AND THE NEUTRINO 199 7 5 COSMIC RAYS 202 7 6 NUCLEAR TRANSFORMATION BY BOMBARDMENT 209 8 WHAT MAKES THE SUN SHINE 215 8 1 CAN GRAVITATIONAL CONTRACTION SUPPLY THE SUN S LUMINOSITY 215 8 2 HOW HOT IS THE CENTER OF THE SUN 217 8 3 NUCLEAR FUSION REACTIONS IN THE SUN S CORE 219 8 3 1 MASS LOST IS ENERGY GAINED 219 8 3 2 UNDERSTANDING THERMONUCLEAR REACTIONS 225 8 3 3 HYDROGEN BURNING 231 8 3 4 WHY DOESN T THE SUN BLOW UP 237 8 4 THE MYSTERY OF SOLAR NEUTRINOS 237 8 4 1 THE ELUSIVE NEUTRINO 237 8 4 2 SOLAR NEUTRINO DETECTORS BURIED DEEP UNDERGROUND 239 8 4 3 SOLVING THE SOLAR NEUTRINO PROBLEM 242 8 5 HOW THE ENERGY GETS OUT 244 8 6 THE FAINT YOUNG SUN PARADOX 252 8 7 THE SUN S DESTINY 253 9 THE EXTENDED SOLAR ATMOSPHERE 255 9 1 HOT VOLATILE MAGNETIZED GAS 255 9 1 1 THE MILLION DEGREE SOLAR CORONA 255 9 1 2 VARYING SUNSPOTS AND EVER CHANGING MAGNETIC FIELDS 258 9 1 3 CORONAL LOOPS 261 9 1 4 WHAT HEATS THE CORONA 266 9 1 5 CORONAL HOLES 268 9 2 THE SUN S VARYING WINDS 268 9 2 1 THE EXPANDING SUN ENVELOPS THE EARTH 268 9 2 2 PROPERTIES OF THE SOLAR WIND 271 9 2 3 WHERE DO THE TWO SOLAR WINDS COME FROM 274 9 2 4 WHERE DOES THE SOLAR WIND END 275 9 3 EXPLOSIONS ON THE SUN 276 9 3 1 SOLAR FLARES 276 9 3 2 CORONAL MASS EJECTIONS 281 9 4 SPACE WEATHER 283 9 4 1 EARTH S PROTECTIVE MAGNETOSPHERE 283 9 4 2 TRAPPED PARTICLES 287 9 4 3 EARTH S MAGNETIC STORMS 288 9 4 4 SOLAR EXPLOSIONS THREATEN HUMANS IN OUTER SPACE 289 9 4 5 DISRUPTING COMMUNICATION 290 9 4 6 SATELLITES IN DANGER 291 9 4 7 FORECASTING SPACE WEATHER 292 10 THE SUN AMONGST THE STARS 293 10 1 COMPARISONS OF THE SUN WITH OTHER STARS 293 10 1 1 HOW FAR AWAY ARE THE STARS 293 10 1 2 HOW BRIGHT ARE THE STARS 296 10 1 3 HOW LUMINOUS ARE THE STARS 298 10 1 4 THE TEMPERATURES OF STARS 303 10 1 5 THE COLORS OF STARS 304 10 1 6 THE SPECTRAL SEQUENCE 305 10 1 7 RADIUS OF THE STARS 306 10 1 8 HOW MASSIVE ARE THE STARS 310 10 2 MAIN SEQUENCE AND GIANT STARS 318 10 2 1 THE HERTZSPRUNG RUSSELL DIAGRAM 318 10 2 2 THE LUMINOSITY CLASS 321 10 2 3 LIFE ON THE MAIN SEQUENCE 323 10 2 4 THE RED GIANTS AND SUPERGIANTS 326 10 3 NUCLEAR REACTIONS INSIDE STARS 329 10 3 1 THE INTERNAL CONSTITUTION OF STARS 329 10 3 2 TWO WAYS TO BURN HYDROGEN IN MAIN SEQUENCE STARS 335 10 3 3 HELIUM BURNING IN GIANT STARS 340 10 4 USING STAR CLUSTERS TO WATCH HOW STARS EVOLVE 343 10 5 WHERE DID THE CHEMICAL ELEMENTS COME FROM 348 10 5 1 ADVANCED NUCLEAR BURNING STAGES IN MASSIVE SUPERGIANT STARS 348 10 5 2 ORIGIN OF THE MATERIAL WORLD 349 10 5 3 THE OBSERVED ABUNDANCE OF THE ELEMENTS 350 10 5 4 SYNTHESIS OF THE ELEMENTS INSIDE STARS 351 10 5 5 BIG BANG NUCLEOSYNTHESIS 353 10 5 6 THE FIRST AND SECOND GENERATION OF STARS 354 10 5 7 COSMIC IMPLICATIONS OF THE ORIGIN OF THE ELEMENTS 355 11 THE MATERIAL BETWEEN THE STARS 357 11 1 GASEOUS EMISSION NEBULAE 357 11 2 SOLID DUST PARTICLES IN INTERSTELLAR SPACE 366 11 3 RADIO EMISSION FROM THE MILKY WAY 369 11 4 INTERSTELLAR HYDROGEN ATOMS 375 11 5 INTERSTELLAR MOLECULES 378 12 FORMATION OF THE STARS AND THEIR PLANETS 381 12 1 HOW THE SOLAR SYSTEM CAME INTO BEING 381 12 1 1 THE NEBULAR HYPOTHESIS 381 12 1 2 COMPOSITION OF THE PLANETS 382 12 1 3 MASS AND ANGULAR MOMENTUM IN THE SOLAR SYSTEM 385 12 2 STAR FORMATION 388 12 2 1 GIANT MOLECULAR CLOUDS 388 12 2 2 GRAVITATIONAL COLLAPSE 389 12 2 3 TRIGGERING GRAVITATIONAL COLLAPSE 392 12 2 4 PROTOSTARS 395 12 2 5 LOSING MASS AND SPIN 398