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					    Recap Astronomical Observations
   What can be observed and measured through the optical
    telescopes ?
   Why is a shirt red ? Why is it black ? Why is the sky blue ?
    (explain in terms of reflection/refraction)
   What is the origin of the black lines in a star’s light spectrum ?
   Explain the meaning of a red-shifted star spectrum.
   What is an interferometer ?
   Describe non-optical astronomy.
   Describe fixed, movable radiotelescopes.
   Describe satellite-based detectors.
   Describe gravitational detectors.
Earth and the Terrestrial Planets

    The moving sky
    Earth structure and atmosphere
    Our Moon and the Earth-Moon system
    Mercury
    Venus
    Mars
            The Moving Sky

   Earth movement: spin(24h), revolution(365.2422d)
   The 23.4o tilt/declination and the seasons
   Motion of the Moon (27.32d)
   Longitude and time
   Calendars: Julian(45 BC), Gregorian (1582 AD)
   Planets orbits and speed: Mercury 48km/s, Earth
    29.8 km.s, Pluto 5km/s.
   Comets: high eccentricity and variable speed
                  Earth Structure
   Earth is more massive than Mars or Venus, has 70% of
    surface covered with water. Density of material doubles as
    one goes to its deeper layers.
   Layers:
      The outer crust has 10-50km (5-10km in ocean beds)
      A mantle of denser rock has 2,900km
      The outer core (iron, nickel) is liquid and has 2,200km
      The inner core is solid and has 1,300km. Temperature
       over 5000o fueled by radioactive disintegrations.
   Geophysicists determine all this from the study of seismic
                Plate Tectonics
   Theory of continental drift (1924)
   Crust+outer mantle(lithosphere) which is rigid and
   Eight large (plus many small) plates flow very slowly on
    top of the inner mantle
   At boundaries magma rises and creates new crust
    structures (ex. mid-Atlantic ridge). In addition
    earthquakes and chains of volcanoes.
   Some short-lived volcanoes appeared in hot spots in the
    middle of a plate (ex. Hawaii islands).
    Earth surface rocks vary in age corresponding to a very
    dynamic history. Water and the wind also shape them.
             Earth Atmosphere

   Composition: nitrogen (78%), oxygen(21%)
   Oxygen is highly reactive and must be replenished –
    photosynthesis uses CO2 to produce oxygen
   CO2 (0.03%) is mainly in limestone and ocean.
    Like water, CO2 contributes to the greenhouse
    effect, which keeps the temperature at an average of
    17o. Without the atmosphere Earth’s surface
    temperature would be –13o. Burning of fossil fuels
    raises the temperature by 0.5o per century.
         Atmospheric Layers
   To 10km troposphere - temperature 17o to –53o
   10-50km stratosphere – temperature raises to -3o
    because ozone (O3) absorbs UV light.
   50-80km mesosphere – temperature drops to –68o
   80-150km thermosphere/ionosphere – temperature
    raises to 800-2000o because of atomic and molecular
    processes with UV and X rays; ions and electrons
    influence radio communications
   To 70,000km magnetosphere – Van Allen belts
    deflect the solar wind and cause auroras at the poles.
                  Our Moon (I)
   With its radius about a quarter of the Earth radius, our
    Moon is the largest relative to the parent except Pluto’s
   Elliptical motion with an average distance of 1.2 light-
    seconds (or 384,400km)
   Surface with cratered highlands (85%) and “seas”(15%).
    Both craters and seas were formed by meteor impact. The
    dark-colored seas correspond to magma spilled after
   Water ice is mixed with rocks at the two poles
   Most likely our Moon was formed through an impact
    between Earth and a similar size body. The same impact
    might be the origin of the tilt in the Earth axis.
Our Moon (II)
        Our Moon Structure
   No atmosphere (too small to keep it)
   1-20m lunar soil (pulverized rocks)
   Below the soil about 65km of lunar crust
   Below the crust about 1,400km of a mantle of
    denser rock
   The lower part of the mantle (at about 800km)
    is partly molten. Minor seismic events are
    generated at that level.
   The center might contain an iron-rich core
    (350km in radius).
       The Earth-Moon System
   Why do we see various lunar shapes ? It is related to
    the relative positions of Earth, Moon and Sun.
   Ocean tides: As a result Earth’s spin slows down
    and the lunar rotation is accelerated. Moon’s spin
    also slowed down and now the fact that its spin is
    synchronized with its revolution results in the fact
    that the same hemisphere is shown to Earth.
   Solar/Lunar Eclipses:
      a solar eclipse is max.7.5 mins.
      Lunar eclipses are less frequent than solar eclipses
       but are seen from the whole hemisphere.
      Max number of eclipses per year is seven.
           Phases of Our Moon
                   half Moon

     full Moon        Earth


Moon phases are related to the shape of the lighted part,
as seen from the observation point on Earth.
                 Other Planets

   The terrestrial planets - Mercury, Venus, Earth
    and Mars - are relatively small, dense with similar
    composition and with solid surfaces.
   The jovian (giant) planets - Jupiter, Saturn,
    Uranus and Neptune - are much larger than Earth.
    Their structure is either a hydrogen-helium gas, or
    a solid icy structure.
   Pluto is a small planet made out of rock and ice.
The Terrestrial Planets: Mercury
   Radius=2,439km, revolution=88d, spin=59d.
   70% iron and 30% rock, but small magnetic field implying
    that most iron is solid. Wrinkles suggest past magma flow;
    impact craters.
   Almost no atmosphere.
   Mercury Signature:
    Day temperature up to 425oC,
    Night temperature -173oC
    But its “day”=59 Earth days
   Observations: Mariner 10 (1974).
    The Terrestrial Planets: Venus

   Radius=6,052km, revolution=225d, spin=243d.
   Structure similar to Earth. Volcanic activity older than on Earth.
   Atmosphere contains 96.5% carbon dioxide and 3.5% nitrogen
    with clouds of sulphuric acid between 5-70km altitude.
   Venus Signature
        The greenhouse effect maintains a constant 480oC.
        It also makes Venus brighter than stars.
   Water and carbon dioxide history different from Earth because
    of distance to the Sun.
   Observations: radar-Mariner 2 (1962), landed - Venera 7 (1970)
    9,10 (1975), radar - Pioneer 12 (1978), Magellan (1994)
     The Terrestrial Planets: Mars
   Radius=3,200km, revolution=687d, spin=24h37m, same axis
    tilt as Earth.
   Mars is the least dense of the terrestrial planets; core contains
    iron and iron sulfide; no magnetic field. Schiaparelli’s polar
    caps and canals (1877), dusty red soil (iron oxides), Olympus
    Mons volcano 25km altitude, Mariner valleys 8km depth,
    dyed-up river beds.
   Although the composition of the atmosphere is similar to
    Venus, its density is about half of Earth’s atmosphere and
    therefore there is no significant greenhouse effect; day 20oC
    and night -70oC; ice clouds, dust storms.
   Possibility of past life (Viking 1976, Antarctica meteorite
    1996). Other missions: Mariner 4 (1965), Mars Pathfinder
    (1997) etc.
Mars Surface

               - Dusty redish soil
               (the “red” planet)
               - The most
               similar to Earth
                Mars Moons
Phobos (R=13.5km) and Deimos (R=7.5km).
 They are captured asteroids.


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