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Planet Earth

Planet Earth. Earth’s Cycles. http://apod.nasa.gov/apod/image/0201/earthrise_apollo8.jpg. Seasons and Sunlight. What is the solar angle of incidence for the equator for the globe on the left? 90 ° 66.5 ° 47 ° 43 °. The globe on the left represents: Summer Solstice Winter Solstice

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Planet Earth

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  1. Planet Earth Earth’s Cycles http://apod.nasa.gov/apod/image/0201/earthrise_apollo8.jpg

  2. Seasons and Sunlight • What is the solar angle of incidence for the equator for the globe on the left? • 90° • 66.5° • 47° • 43° • The globe on the left represents: • Summer Solstice • Winter Solstice • Equinox and cannot tell if it is the spring or fall • Not enough information http://www.physicalgeography.net/fundamentals/images/earth_sun_angles.gif

  3. Seasons and Sunlight • What is the solar angle of incidence for the equator for the globe on the right? • 90° • 66.5° • 47° • 43° • The globe on the right represents: • Summer Solstice • Winter Solstice • Equinox and cannot tell if it is the spring or fall • Not enough information http://www.physicalgeography.net/fundamentals/images/earth_sun_angles.gif

  4. Direction of Rotation A B • If you are looking down at the North Pole, does the earth spin • Counterclockwise • Clockwise http://www.flutrackers.com/forum/attachment.php?attachmentid=1512&d=1176083504

  5. Eccentricity • 100,000 year cycle • Winter in North at Perihelion, and therefore shorter than summer • Low eccentricity of 0.005 • High eccentricity of 0.058 • Mean eccentricity of 0.028 • Present eccentricity 0.017 • Moving towards low centricity - warming Perihelion Aphelion http://en.wikipedia.org/wiki/File:Eccentricity_half.svg

  6. Obliquity • Tilt of the Axis • 41,000 year cycle • Minimum tilt is 21.1º • Maximum tilt is 24.5º • Currently at 23.5º • Tilt is decreasing - cooling http://upload.wikimedia.org/wikipedia/commons/6/61/AxialTiltObliquity.png

  7. Precession • Wobble like a top • Completes the wobble every ~21,000 years • Other “north stars, Thuban in Draco and Vega in Lyra • Top 10 sec • Both 33 sec http://stardate.org/images/gallery/d_procession.jpg

  8. Milankovitch Cycles • These three cycles, in combination, can alter climate • Eccentricity • Obliquity • Precession • Milankovitch 2.38 min http://www.cgd.ucar.edu/research/highlights/section/milankovitch.jpg

  9. Questions?

  10. Earth/Moon/Sun System • Milankovitch Cycles – Eccentricity – Earth’s distance from the sun varies, with an average of 93,000,000 miles • Johannes Kepler’s 2nd law of Equal Areas • Sweep http://outreach.atnf.csiro.au/education/senior/cosmicengine/images/cosmoimg/kepler2ndlaw.gif

  11. The Moon • Large Satellite Hypothesis • planetary habitability is enhanced by the presence of a large satellite • axial stability of a planet also enhances habitability http://www.dailyflier.com/astro/earth-mars.JPG

  12. The Moon • Compare to Mars • Moons of Mars are so small, they cannot form a sphere • Deimos (dread) smaller and further satellite • Phobos (fear) larger and closer satellite Phobos Deimos http://upload.wikimedia.org/wikipedia/commons/2/23/Mars_Moons_Orbit_distance_flipped.jpeg http://www.lpi.usra.edu/expmars/activities/phobosFS.gif http://www.astro.keele.ac.uk/~rdj/planets/images/Deimos-viking1.jpg

  13. The Moon • Formation of the moon • Before 1969, hypotheses why Earth had such a large satellite • Fission Hypothesis • Capture Hypothesis • Co-Formation Hypothesis • Giant Impact Hypothesis • NoMoon (2.14 min) http://exoplanet.as.arizona.edu/~lclose/teaching/a202/lect5.html

  14. The Moon • Lunar Landings • Returned with moon rocks • Composition of rocks similar to surface of Earth • Best fit hypothesis, Giant Impact Hypothesis • Angular Momentum • Composition of Moon • Age of Rocks (younger than Earth by ~100-300 million years) • Scale (<2 sec) http://www.fas.org/irp/imint/docs/rst/Sect19/moonsim.jpg

  15. The Moon • Gravitation pull of Moon (also pulls land) • Centrifugal forces – barycenter is pivotal point • Centrifugal (17 sec) • Centrifugal1 (7.27 min) • Tide (20 sec) • Tide2 (55 sec) http://www.lhup.edu/~dsimanek/scenario/tides.htm

  16. Earth/Moon System • Rotation of the Earth Moon around the barycenter (<10 sec) • Pivot is around the barycenter and not through the center of the Earth http://library.thinkquest.org/29033/begin/earthsunmoon.htm

  17. Astronomical events Within galactic habitable zone Supernovae to seed our system Sun the “right” size Within solar system’s habitable zone Large gas giants Large satellite (Moon) Occasional bolides strikes Geologic events Size of Earth Dynamo Earth forms magnetic poles Magnetosphere Plate tectonics Atmosphere Lithosphere Oceans (water terrestrial or extraterrestrial?) Glaciations Rare Earth Hypothesis

  18. Intelligent life is common throughout the universe because, as Carl Sagan would say, the universe is a very big place Assumes that the Earth’s life is a common occurrence Assumes that if life occurs, then rational life will form with advanced technology Drake Equation: N = N* fp ne fl fi fc fL N* # of stars in the Milky Way Galaxy (125-500 billion) fp fraction of stars that have planets (20 – 50%). ne # planets/star capable of sustaining life (1 to 5) fl fraction of planets in ne where life evolves (0-100%) fi fraction of fl where intelligent life evolves (0-100%) fc is the fraction of fi that communicate (10 – 20% fL fraction of the planet's life during which the communicating civilizations live (1/1,000,000th) N, the number of communicating civilizations in the galaxy. Mediocrity Principle

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