HNRS 227 Lecture #16 & 17 Chapters 12 and 13

1. HNRS 227 Lecture #16 & 17Chapters 12 and 13 The Universe and Solar System presented by Prof. Geller 21 and 23 October 2003

2. Key Points of Chapter 12 • Historical Views • 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

3. Key Points of Chapter 12 • 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

4. Key Points of Chapter 12 • 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

5. Key Points of Chapter 12 • 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

6. The Hertzsprung-Russell (HR) Diagram

7. The Life Story of Stars Surface • 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 Gravity Weight of outer layers Gas Pressure Thermal Energy Center

8. Post Main Sequence Evolution Helium burning Heium “Burning” 4He2 + 4He2  8Be4 8Be4 + 4He2  12C6 +  12C6 + 4He2  16C8 + 

9. Evolution from Giants to Dwarfs

10. Stellar Evolution by Mass Main sequence stars Supergiants Giants Helium flash C detonation Heavy nuclei fusion Supernovae Planetary nebulae Black holes Ns White dwarfs 40 10 4.0 0.1 100 1.0 0.4 Mass (MSun = 1)

11. 25 Msun Star Evolution

12. Key Points of Chapter 12 • Galaxies • our own Milky Way • different types • elliptical, spiral, barred spiral • Hubble’s Law • Cosmology

13. 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

14. Hubble’s Law • The further away a galaxy is, the greater its recessional velocity and the greater its spectral red shift

15. 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

16. Big Bang Summary

17. Key Points of Chapter 13(some of which was eliminated) • Geocentric solar system • Ptolemaic model • Heliocentric solar system • Copernican model • Kepler’s Laws of Planetary Motion • Origin of Solar System • Overview of Planets

18. 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

19. 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

20. Other Planet Observations • Terrestrial planets are closer to sun • Mercury • Venus • Earth • Mars • Jovian planets furthest from sun • Jupiter • Saturn • Uranus • Neptune

21. Other Observations • Radioactive dating of solar system rocks • Earth ~ 4 billion years • Moon ~4.5 billion years • Meteorites ~4.6 billion years • Most orbital and rotation planes confined to ecliptic plane with counterclockwise motion • Extensive satellite and rings around Jovians • Planets have more of the heavier elements than the sun

22. A Linear View of Abundance

23. Log Abundance of Elements

24. Planetary Summary

25. 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

26. 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

27. Nebular Condensation Chemistry

28. Key Points of Chapter 13(some of which was deleted) • 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

29. Key Points of Chapter 13(all eliminated from 2nd edition) • The Moon • phases of the Moon • Eclipses • lunar • solar