ASTRONOMY 161 Introduction to Solar System Astronomy

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ASTRONOMY 161Introduction to Solar System
Astronomy
Class 15
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Midterm 2 (Friday, in class)

• 1) Use the study guide.
• 2) Know and understand the basic equations.
• 3) Only material covered in class is required.
• 4) Laws of motion are important.
• 5) Properties of light are important.
• Good luck!

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Midterm Exam Sample Question

• The masses of planets are measured from
  
• A) their brightness.
  
• B) their size and density.
  
• C) acceleration their gravity produces on nearby
  objects.
  
• D) infrared and radio emission.
  
• E) their resistance to being gravitationally
  accelerated.

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Midterm Exam Sample Questions

• Name the planet which comes closest to the Earth
  (26 million miles)
  
• A) Saturn
  
• B) Jupiter
  
• C) Venus
  
• D) Uranus
  
• E) Mercury

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The Earth Wednesday, October 27
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The Earth Physical characteristics

• Mass 5.971024 kg
• Mean radius 6,373 km
• Polar radius 6,357 km
• Density 5,515 kg/m³
• Sidereal rotation period 0.9973 d (23.934 h)
• Axial tilt 23.4

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The Earth Key Concepts

• (1) The study of seismic waves tells us about the
  Earths interior.
• (2) The Earth is layered into crust, mantle,
  inner core, and outer core.
• (3) The Earth is layered because it underwent
  differentiation when molten.
• (4) The lithosphere is broken into plates that
  move relative to each other.
• (5) The motion of liquid metal in the outer core
  produces a magnetic field.

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(1) The study of seismic waves
tells us about the Earths interior.

• How can we study the deep interior of the Earth?
• Average density of the Earth 5500 kg/m3
• Earth is too dense to be solid rock
  Basalt 3300 kg/m3 Granite
  2700 kg/m3

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• Earthquakes produce two types of seismic waves
• P waves Primary, Pressure Sound waves travel
  through solids and liquids.
• S waves Secondary, Shear Transverse
  (side-to-side) waves that do NOT travel through
  liquids.

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• Seismic waves radiating through the Earth after
  an earthquake
• Note S waves do not travel through the outer
  core!

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(2) The earth is layered into a crust, mantle,
inner core, and outer core.

• From the outside in
• 1) Crust
  solid rock
  5 km
  thick basalt (ocean floor)
  35 km thick granite (continents)
• 2) Mantle
  partly solid rock, partly semisolid
  (plastic) rock 2900 km thick

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• 3) Outer (liquid) core
  molten iron and nickel
  2200 km thick
• 4) Inner (solid) core
  solid iron and nickel
  1300 km in radius

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• The center of the Earth is as hot as the surface
  of the Sun.
• Why doesnt the inner core melt??
• The high pressure in the inner core keeps it
  solid.

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(3) The Earth is layered because it underwent
differentiation when molten.

• When young, the Earth was heated by the impact of
  planetesimals. For a while, the Earth was molten.
• In a liquid, dense stuff sinks, low-density stuff
  floats.

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• When differentiation was complete, Earth cooled
  and (partly) solidified.
• Crust of the ocean floor floats on the mantle
  like skin on cocoa lower-density continents
  are the marshmallows.

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(4) The lithosphere is broken into plates
that move relative to each other.

• The crust plus the upper mantle form the
  lithosphere (solid but brittle).
• Beneath the lithosphere is the asthenosphere
  (plastic).
• The asthenosphere, heated from below,
  undergoes convection.

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Convection
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• Convection currents in the asthenosphere have
  broken the lithosphere into sections called
  plates.
• There are 15 large plates.

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• Continuing convection in the asthenosphere causes
  plates to move relative to each other.
• The study of plate motion is called plate
  tectonics.
• The motion of continents
  was first suspected by
  Sir Francis Bacon
  (17th cent). Best
  known for leading the
  scientific revolution with his
  new 'observation and
  experimentation' theory.

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• America and Europe are moving apart by 3
  centimeters per year ( 30 km per million
  years).
• This continental drift is measured using GPS
  (global positioning systems).

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• 200 million years ago, the Americas, Europe, and
  Africa formed a single supercontinent, PANGAEA.

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• The boundaries between plates are geologically
  active, with many volcanoes and earthquakes.
• Example the Ring of Fire around the Pacific
  Ocean.

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• Types of plate boundaries
• 1) Oceanic rift plates moving apart, new rock
  forming.
• 2) Subduction zone plates moving together, ocean
  crust shoved under continent.
• 3) Mountain-building zone plates moving
  together, continents collide buckle upward.
• 4) Transverse fault plates slipping past each
  other, with lots of friction.

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• The summit of Mount Everest is made of marine
  limestone.
• It has been lifted
  9 kilometers
  high!

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• Grand Tetons

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• Grand Tetons

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• The San Andreas
  transverse fault
• Motion jumps
  during a quake

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(5) The motion of liquid metal in the outer core
produces a magnetic field.

• A compass points to the Earths North Magnetic
  Pole (not the true North Pole!)
• Why is the Earth a giant magnet?

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• Remember Moving charged particles create a
  magnetic field.
• Inside the Earth, convection currents exist
  within the liquid outer core. These currents
  carry electrons around, creating a magnetic field.

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• The Earths magnetic field stretches far beyond
  the surface.
• Our magnetic field deflects the solar wind
  (electrons and protons streaming away from the
  Sun).

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Few closing questions

• 1) Are there earthquakes in Ohio?
• 2) Are there any volcanoes in Ohio?
• 3) Why is Ohio so boring?
• 4) If you are at the North Pole, which way does
  the compass needle point?