Integrative Studies 410 Our Place in the Universe

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INST 410 Our Place in the Universe
The Earth-Moon system
gburk_at_otterbein.edu

• Secretary Sandra Salee (x1316)
• FAX [phone]
• OfficeHours by appointment.

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The Earth-Moon System
Earth/Moon radius ¼ Earth/Moon mass
1/81 Earth-Moon distance 384,000 km
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Features of the Earth

• Mass 6 ? 1024 kg
• Radius 6400 km
• Density 5500 kg/m3
• Water density 1000 kg/m3
• Surface rock density 2000-3000 kg/m3
• Distance to moon 384,000 km (250,000 mi)
• Period of rotation 1 day
• Period of revolution 1 year

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Structure of the Earth

• Core
• Mostly iron and nickel
• Inner core solid, outer core liquid
• Mantle
• Mostly basalt, a heavy mineral containing iron
  and magnesium
• Soft can flow even though it is solid rock
• Crust
• Solid surface layer floats on the mantle

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Structure of the Earth

• Density and temperature both increase with depth
• Crust
• Average thickness 15 km
• Mantle
• Average thickness 3000 km
• Core
• Inner cores radius 1300 km
• Outer cores radius 3500 km
• T 6000 K, similar to that of the Sun!

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Surface Features
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Earths Surface Dynamics

• Continental plates drift apart
• hot magma comes to surface ? Volcanism
• Volcanic islands Hawaii, Lanzarote (Spain)

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Earths Changing Surface
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Earths Atmosphere

• 78 Nitrogen, 21 Oxygen, 1 Other
• Troposphere region of weather
• Stratosphere stable and calm
• Ionosphere gases charged by interaction with
  radiation from space

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Ozone Layer (O3)

• Absorbs most UV radiation from the Sun
• Hole over Antarctic
• Chlorofluorocarbons (CFCs) released by spray
  cans, refrigerators
• Latest pictures indicate the hole is bigger than
  ever!

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Greenhouse Effect

• Earth absorbs energy from the Sun and heats up
• Earth re-radiates the absorbed energy in the form
  of infrared radiation
• The infrared radiation is absorbed by carbon
  dioxide and water vapor in the atmosphere

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Magnetosphere

• Magnetic north pole about 7 west of geographic
  north pole

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Motion of Charged Particles
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Van Allen Radiation Belts

• Mainly heavier protons in the inner belt
• electrons in outer belt

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Aurora Borealis
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Aurora Borealis from Space
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Features of the Moon

• Mass 1/81 Earths mass
• Radius 1/4 Earths radius
• Density 3,300 kg/m3
• Gravity 1/6 Earths gravity
• Period of revolution 1 month
• Period of rotation 1 month
• Synchronous rotation

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Large-Scale Features

• Maria
• Dark areas resembling oceans
• Plains of solidified lava
• Part of the lunar mantle
• About 3.23.9 billion years old
• Highlands (Terrae)
• Light-colored, resemble continents
• The lunar crust
• More than 4 million years old

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The Moon Far Side

• Can be seen by satellites only

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The Mountains of the Moon

• Especially well visible near the terminator the
  borderline between light and shadow

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Moon from our Observatory I

• Through 8 inch telescope, 40 mm eyepiece, Sony
  DSC 717 digital camera, December 31, 2003

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Moon from our Observatory II

• Through 8 inch telescope, 40 mm eyepiece, Sony
  DSC 717 digital camera, December 31, 2003

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Moon from our Observatory III

• Through 8 inch telescope, 40 mm eyepiece, Sony
  DSC 717 digital camera, December 31, 2003

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A Lunation of 28.5 days
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The Moon - Touchdown

• Note the soft edges of the crater ?Erosion!
• Traces of the Apollo lunar rover

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Structure of the Moon

• Also consists of crust, mantle and core
• No hydrosphere, magnetosphere or atmosphere
• Little seismic action

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Tides

• Daily fluctuations in the ocean levels
• Two high and two low tides per day
• A result of the difference in gravitational pull
  from one side of the Earth to the other
• F G M m / R2

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Tides

• Earths rotation drags the tidal bulge with it
• Friction causes the Earths rotation to slow (by
  0.002 seconds every century), and the moon to
  spin away from Earth (about 4 cm every century)

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Spring and Neap Tides

• Tides especially pronounced when sun and moon
  work together
• Same direction ? Spring tide
• Other direction ? Neap tide

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Lunar Craters

• Old scars from meteoroid impacts
• Lots of them all sizes
• Copernicus 90 km across
• Reinhold 40 km across
• Also craters as small as 0.01 mm!

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(Almost) Catastrophic Impacts

• Orientale Basin
• Almost 1000 km diameter
• A somewhat larger impact body could have
  destroyed the moon!

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How They Form
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Moons Changing Surface
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Ages of the Earth and Moon

• Determined by radioactive dating
• Compare amount of radioactive material with
  amount of decay product
• Useful isotopes
• Uranium-238 (half-life 4.5 billion years)
• Uranium-235 (half-life 0.7 billion years)
• For shorter time scales, Carbon-14 (5730 years)
• Oldest surface rocks on Earth (Greenland,
  Labrador) about 3.9 billion years old
• When rocks solidified
• Lunar highlands 4.14.4 billion years old
• Rocks from lunar maria slightly younger, more
  recently melted
• Meteorites 4.5 billion years old
• Date to origin of solar system

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Creation of the Earth-Moon system

• Sister theory Earth and Moon formed at same
  time in the same part of the solar system (but
  they have different compositions??)
• Capture theory Earth captured the Moon as it
  passed by need not have the same composition
  (but gravitational capture is improbable)
• Daughter or fission spinning Earth threw off
  the Moon (but how did it get to be spinning that
  fast?)
• Impact theory large body hits the (molten)
  Earth and is absorbed part of Earth's mantle is
  knocked out. (Plausible supported by computer
  simulations but there's no direct evidence!)

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Impact (Big Whack) Theory
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