HNRS 227 Lecture

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HNRS 227 Lecture 15-17Chapters 16, 17 and 18

• The Universe and Solar System
• presented by Prof. Geller
• 17,22,24 October 2002

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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

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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

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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

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Key Points of Chapter 16

• Temperature of stars
• Wiens Law
• spectral classes based upon temperature
• not linear scale
• H-R Diagram
• temperature versus absolute brightness
• following the evolution of stars

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The Hertzsprung-Russell (HR) Diagram
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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

Surface
Luminosity
Gravity
Weight of outer layers
Gas Pressure
Thermal Energy
Center
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Post Main Sequence Evolution
Helium burning
Heium Burning 4He2 4He2 ? 8Be4 8Be4
4He2 ? 12C6 ? 12C6 4He2 ? 16C8 ?
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Evolution from Giants to Dwarfs
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Stellar Evolution by Mass
Main sequence stars
Supergiants
Giants
Helium flash
C detonation
Heavy nuclei fusion
Supernovae
Planetary nebulae
Ns
Black holes
White dwarfs
0.1
4.0
10
40
100
0.4
1.0
Mass (MSun 1)
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25 Msun Star Evolution
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Key Points of Chapter 16

• Galaxies
• our own Milky Way
• different types
• elliptical, spiral, barred spiral
• Hubbles Law
• Cosmology

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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

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Hubbles Law

• The further away a galaxy is, the greater its
  recessional velocity and the greater its spectral
  red shift

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Hubbles Conculsion

• From Hubbles 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

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Key Points of Chapter 17

• Geocentric solar system
• Ptolemaic model
• Heliocentric solar system
• Copernican model
• Keplers Laws of Planetary Motion
• Origin of Solar System
• Overview of Planets

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Keplers Laws of Planetary Motion

• Keplers First Law of Planetary Motion
• planets orbit sun in an ellipse with sun at one
  foci
• Keplers Second Law of Planetary Motion
• planets sweep out equal areas in equal times
• travel faster when closer, slower when farther
• Keplers Third Law of Planetary Motion
• orbital period squared is proportional to
  semi-major axis cubed
• P2 a3

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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

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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

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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

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Nebular Condensation Chemistry
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Key Points of Chapter 18

• Earths Motions
• revolution
• about Sun
• rotation
• on its axis
• Reason for the seasons
• tilt of the Earths axis
• Measuring time
• hours, minutes, seconds

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Key Points of Chapter 18

• The Moon
• phases of the Moon
• Eclipses
• lunar
• solar
• Tidal Effects