Astronomy 204 Lecture 4 The Solar System in Perspective

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Astronomy 204Lecture 4The Solar System in
Perspective
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Lecture Outline

• Solar System Overview
• Planet motions
• Planet interiors
• Planet surfaces
• Planetary Atmospheres

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Our Solar system is disk-shaped and all planets
have a common direction of revolution.
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Observing the Solar Plane
An observer looking west just after sunset can
easily observer the disk-shaped nature of the
solar system through the positions of the
planets.
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What is a Planet?

• A celestial body that is orbit around the Sun
• Has enough mass/self-gravity to make itself into
  a round or mostly round shape
• Has cleared the neighborhood around its orbit

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And the other stuff?

• Dwarf Planet
• meets requirements of planet except it hasnt
  cleared its neighborhood
• Include Pluto and Ceres
• Small Solar System body
• All other stuff that isnt a moon

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Most planets in our solar system have a common
direction of rotation.
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Orbits of the Planets are very close to being
circular and there are two Scales in our Solar
System.
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Terrestrial Jovian Planets
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Graph of Planetary Masses
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Graph of Planetary Diameters
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Graph of Planetary Densities
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Graph of Planetary Rotation Periods
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Doppler Effect for finding Rotation Periods
Bouncing Radar pulses off Planets
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Resonance
PRotation 59 days PRevolution 88 days a 23
resonance -- meaning that Mercury revolves twice
for every three times it rotates. This is due to
the long history of gravitational interactions
with the sun. This slow rotation leads to a
tremendous temperature differential between the
side facing the sun (700 K) and the dark side
(100 K).
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Interiors

• Planetary masses M are determined by applying
  Keplers third law to satellite orbits
• Planetary radii R are determined largely through
  occultations
• We can now calculate the mean density
• Settling (differentiation) has occurred on
  terrestrial planets