Planetary Configurations

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The Illusion of changing Lunar Size
Sequence of photos over Seattle, with the final
one a longer exposure
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Synodic vs Sidereal for the Moon
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View of the Moons Orbit
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Attributes of the Earth-Moon System
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Making Eclipses
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Anatomy of Solar Eclipses
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Eclipse Tracks
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Baileys Beads
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Lunar Eclipses
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A Lunar Eclipse
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Share Question

• In order for a solar eclipse to occur, the Moon
  must be
• a) high in the sky
• b) near first or last quarter
• c) near new moon
• d) near full moon
• e) over another country

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Sequence of Lunar Phases
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Orbital View of Lunar Phases
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Geometry of Lunar Phases Earth Perspective
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Snapshots of Lunar Phases What doesnt change?
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Lunar Rotation
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Share Question

• As seen from the Moon, how often does the Sun
  rise?
• a) Never.
• b) About every 24 hours.
• c) About once per week.
• d) About once per month.
• e) About once per year.
• As seen from the Moon, how often does the Earth
  set?
• a) Never.
• b) About every 24 hours.
• c) About once per week.
• d) About once per month.
• e) About once per year.

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Prominent Lunar Missions

• Luna 3 1959, Soviet
• 1st pictures of Moons far side
• Apollo 11 July 20, 1969
• Astronauts Armstrong, Aldrin, and Collins
  first on Moon
• Apollos 11-17 1969-1972
• Returned 400 kg of Lunar samples
• Moon exploration continues to search for water
  and to study its structure

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Soviet Commemorative Stamps
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Dark Side of the Moon
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Apollo 11
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Buzz Aldrin
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Flag on the Moon
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Lunar Footprint
Mare Basalt
Highland Breccia
Highland Anorthosite
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Water Ice on the Moon

• Lunar probes Clementine and Lunar Prospector
  have provided suggestive evidence for the
  existence of water ice in permanent shadows near
  the lunar poles.

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Water Found on the Moon

• Four spacecraft recently reported small amounts
  of H2O and/or OH at the Moon
• Indias Chandrayaan mission
• NASAs Cassini mission
• NASAs EPOXI mission
• NASAs LCROSS mission
• The first three measured the top few mm of the
  lunar surface. LCROSS measured plumes of lunar
  gas and soil ejected when a part of the
  spacecraft was crashed into a crater.
• How much water? Approximately 1 ton of lunar
  regolith will yield 1 liter of water

This false-color map created from data taken by
NASAs Moon Mineralogy Mapper (M3) on Chandrayaan
is shaded blue where trace amounts of water (H2O)
and hydroxyl (OH) lie in the top few mm of the
surface.
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How was Water Detected?

• Lunar soil emits infrared thermal radiation. The
  amount of emitted light at each wavelength varies
  smoothly according to the Moons temperature.
• H2O or OH molecules in the soil absorb some of
  the radiation, but only at specific wavelengths
• All four infrared spectrographs measure
  absorption by water.

model with thermal radiation only
model with thermal radiation and absorption by
molecules
An infrared spectrum measured by LCROSS (black
data points) compared to models (red line)
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The Big Picture

• Lunar water may come from solar wind hydrogen
  striking the surface, combining with oxygen in
  the soil. It may also arrive via meteorite and
  comet impacts. Both processes are likely.
• Lunar water may be bounced by small impacts to
  polar regions, forming ice in permanently
  shadowed craters
• Similar processes may occur on other airless
  bodies (e.g., Mercury, asteroids)
• Water-laden lunar regolith may be a valuable
  resource, possibly supporting future lunar
  exploration activities

Discovery of water on the moon may support future
activities on the lunar surface and beyond.
Artwork from NASA / Pat Rawlings.
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Tidal Forces

• Tidal forces are a consequence of how gravity
  from one body acting on a second body varies
  across that second body.
• Gravity is
• A vector
• Changes with distance
• Both Moon and Sun contribute to tides at the
  Earth (Suns tidal force about half of Moons)
• Spring tide - when they add up (Sun, Earth, and
  Moon aligned at New and Full phases)
• Neap tide - when tides are at odds (1st qtr. and
  3rd qtr. Lunar phases)

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The Tidal Force
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Lunar Deformation

• This is a false-color plot of the Moons
  deviation from spherical shape. Blue is
  squashedness (near the poles) and red is
  stretchedness (mostly at front and rear faces).
  Based on data from Clementine.

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Roche Limit

• Gravity scales like, FG 1/r2
• Tidal forces scale like, FT 1/r3
• Different dependence on distance suggests that
  tidal forces (although weak) could overcome
  surface gravity at some close distance, which is
  called the Roche Limit
• One kind of Roche Limit is to ask how close a
  moon must come to a planet before the tidal force
  of the planet lifts a rock off the surface of the
  moon.

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The Roche Limit
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Tidal Evolution of Lunar Orbit
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Lunar Surface

• Regolith layer of rock and dust debris built up
  from meteoritic impacts
• Mare few craters
• Terrae many craters
• Galileo discovered Lunar craters in 1609
• Craters
• Reveals properties of sub-surface
• Amount of cratering related to surface age

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Stretch of Lunar Terrain
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Lunar Climate

• The escape speed from the Moon is 2.3 km/sec, and
  so it has essentially no permanent atmosphere
• Moon does keep a transient atmosphere from
  capture of solar wind and radioactive decay in
  rocks (composition mainly He, Ne, Ar, and H)
• Without an atm., the sky is always black, and
  there are large day-night temperature swings,
  from 400 K (260 F) to 100 K (-280 F)
• Earth has a 20 K (36 F) temperature swing on
  average

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Crater Formation

• FEATURES
• Impact produces a crater
• Sprays ejecta
• Often leaves a rim
• Sometimes with associated bright rays (radial
  spokes, possibly a consequence of color
  contrast)

• Impact converts kinetic energy to thermal,
  acoustic, and mechanical energy
• melting
• thudding
• wrecking

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Crater Formation
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Share Question

• Why are some large crater walls sharp and steep,
  while others are more rounded?
• a) different volcanos make different
  craters
• b) age differences
• c) size differences among the impact
  bodies
• d) composition differences among the
  impact bodies
• e) seismic activity on the Moon

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The Copernicus Crater
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Rays
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Crater Dating

• Count number of craters, divide by cratering
  rate, get an age!
• CAUTIONS
• Erosion
• Cratering rate can vary over time
• Crater saturation overcrowding (craters upon
  craters)
• NOTE Erosion can also bias relative numbers of
  different sized craters, since smaller craters
  tend to get erased faster.

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Moons Interior
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Origin of the Moon

1. The Moon is old.
2. The chemical composition of the Moon and Earth is
   similar but not identical.
3. Near absence of the iron core in Moon.
4. The Moons orbit is inclined to the Earths
   equator, somewhat inclined to the ecliptic, and
   is prograde.

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Models

• Fission Theory
• Moon spun off from rapidly rotating Earth
  after iron core formed
• Binary Accretion Theory formed as a pair

• Capture Theory having formed elsewhere, the
  Moon was captured in a close encounter
• Giant Impact Theory collision between
  Mars-sized body and Earth debris collects to
  form our Moon

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Model Schematics
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Challenges

• Fission
• Moons orbit inclined to Earth equator
• Needed rotation at once per 4 hrs why was Earth
  so fast?
• Binary
• why no iron in Moon?

• Capture
• Capture difficult (how to slow down?)
• Are Earth and Moon compositions too similar?
• Giant Impact
• favored

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Artistic Impression of Giant Impact
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Giant Impact Theory

1. Similar composition to Earth because debris
   contains mantle material
2. Different composition owing to the impacting body
3. Moons orbit being inclined is not surprising
4. Body was iron-poor and Earths iron core was
   already formed