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HNRS 227 Lecture #15-17 Chapters 16, 17 and 18 The Universe and Solar System presented by Prof. Geller 17,22,24 October 2002 Key Points of Chapter 16 Historical Views (also in Chapter 17) geocentric model of the universe Ptolemaic Model heliocentric model of the universe Copernican Model Coordinate Systems Local Horizon System altitude, azimuth Celestial Coordinate System right ascension, declination Key Points of Chapter 16 Measurements angular degrees 1 degree = 60 minutes = 3600 seconds hour-angle one hour is 15 degrees of arc light year distance traveled by light in a year Astronomical Unit (AU) mean distance of Earth to Sun Key Points of Chapter 16 Main Sequence Stars core, radiation zone, convection zone, photosphere Magnitude Scale log scale lower value brighter (x 2.5) than higher value absolute versus apparent absolute is magnitude at 10 parsecs Key Points of Chapter 16 Temperature of stars Wien’s Law spectral classes based upon temperature not linear scale H-R Diagram temperature versus absolute brightness following the evolution of stars The Hertzsprung-Russell (HR) Diagram The Life Story of Stars Gravity squeezes Pressure forces resist Kinetic pressure of hot gases Repulsion from Pauli exclusion principle for electrons - white dwarf Repulsion from Pauli exclusion principle for neutrons - neutron star None equal to gravity - black hole Energy loss decreases pressure Energy generation replaces losses Star is “dead” when energy generation stops White dwarf, neutron star, black hole Luminosity Surface Gravity Weight of outer layers Gas Pressure Thermal Energy Center Helium burning Post Main Sequence Evolution Heium “Burning” 4He 2 + 4He2 8Be4 8Be 4 + 4He2 12C 12C + 4He2 16C 6 6 8 + + Evolution from Giants to Dwarfs Stellar Evolution by Mass Main sequence stars Supergiants Giants Helium flash C detonation Heavy nuclei fusion Supernovae Planetary nebulae Black holes Ns White dwarfs 100 40 10 4.0 Mass (MSun = 1) 1.0 0.4 0.1 25 Msun Star Evolution S ta g e Hydrogen burning Central Temperature (K ) 7 4 x 10 Helium burning 2 x 10 8 7 x 10 2 5 x10 year Carbon burning 6 x 10 8 2 x 10 5 600 year Neon burning 1.2 x 10 9 4 x 10 6 1 year Oxygen burning 1.5 x 10 9 1 x 10 7 6 months Silicon burning 2.7 x 10 9 3 x 10 7 1 day Core collapse 5.4 x 10 9 3 x 10 9 0.2 seconds Core bounce 2.3 x 10 10 4 x 10 14 milliseconds Explosion About 10 9 Central Density 3 (g/cm ) 5 Varies Duration of stage 6 7 x10 year 5 10 seconds Key Points of Chapter 16 Galaxies our own Milky Way different types elliptical, spiral, barred spiral Hubble’s Law Cosmology Recall the Doppler Shift A change in measured frequency caused by the motion of the observer or the source classical example of pitch of train coming towards you and moving away Hubble’s Law The further away a galaxy is, the greater its recessional velocity and the greater its spectral red shift Hubble’s Conculsion From Hubble’s Law we can calculate a time in the past when universe was a point Big bang occurred about 15 billion years ago big bang first proposed by George Gamow based upon such evidence big bang named by antagonist Fred Hoyle who preferred the steady-state model Key Points of Chapter 17 Geocentric solar system Ptolemaic model Heliocentric solar system Copernican model Kepler’s Laws of Planetary Motion Origin of Solar System Overview of Planets Kepler’s Laws of Planetary Motion Kepler’s First Law of Planetary Motion planets orbit sun in an ellipse with sun at one foci Kepler’s Second Law of Planetary Motion planets sweep out equal areas in equal times travel faster when closer, slower when farther Kepler’s Third Law of Planetary Motion orbital period squared is proportional to semi-major axis cubed • P2 = a3 Planetary Observations Planets formed at same time as Sun Planetary and satellite/ring systems are similar to remnants of dusty disks such as that seen about stars being born Planet composition dependent upon where it formed in solar system Nebular Condensation (protoplanet) Model Most remnant heat from collapse retained near center After sun ignites, remaining dust reaches an equilibrium temperature Different densities of the planets are explained by condensation temperatures Nebular dust temperature increases to center of nebula Nebular Condensation Physics Energy absorbed per unit area from sun = energy emitted as thermal radiator Solar Flux = Lum (Sun) / 4 x distance2 Flux emitted = constant x T4 [Stefan-Boltzmann] Concluding from above yields T = constant / distance0.5 Nebular Condensation Chemistry Molecule H2 H2O CH4 NH3 FeSO4 SiO4 Freezing Point Distance from Center >100 AU 10 K >10 AU 273 K >35 AU 35 K >8 AU 190 K >1 AU 700 K >0.5 AU 1000 K Key Points of Chapter 18 Earth’s Motions revolution about Sun rotation on its axis Reason for the seasons tilt of the Earth’s axis Measuring time hours, minutes, seconds Key Points of Chapter 18 The Moon phases of the Moon Eclipses lunar solar Tidal Effects