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The Moon

The Moon. Astronomy 311 Professor Lee Carkner Lecture 13. Temperature of Earth. Temp of Earth from energy balance T E = [R S /(2 D S )] ½ T S T E = [6.96X10 8 / (2)(1.496X10 11 )] ½ (5778) T E = 278.7 K T F = 1.8T K -460 = (1.8)(278.7)-460 T F = 41.6 F Actual Earth temp = 288 K

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The Moon

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  1. The Moon Astronomy 311 Professor Lee Carkner Lecture 13

  2. Temperature of Earth • Temp of Earth from energy balance • TE = [RS/(2 DS)]½ TS • TE = [6.96X108 / (2)(1.496X1011)]½ (5778) • TE = 278.7 K • TF = 1.8TK -460 = (1.8)(278.7)-460 • TF = 41.6 F • Actual Earth temp = 288 K • T = (1.8)(288)-460 = 58.4 F • Earth has an atmosphere, not all of the energy radiated by the Earth gets out

  3. Temperature of Earth • How much energy does Earth emit? • P = sAT4 = s4pRE2T4 • P = (5.67X10-8)(4p)(6.38X106)2(288)4 • P = 1.995X1017 W • What happens if diameter of Earth doubles? • Earth emits more energy • But, Earth also absorbs more energy • T does not depend on Earth size • TE = [RS/(2 DS)]½ TS

  4. Luna -- The Goddess of the Moon • Since ancient times the Moon has been thought to affect behavior (“lunatic”, “moonstruck”) • There is no good evidence for this however

  5. Principle Features of the Moon • Maria • maria is Latin for seas • arrangement of maria produces the “man-in-the-moon” • Highlands • Craters • circular impact structures • range in size from few hundred km to microscopic

  6. Moon Facts • Size: 3476 km diameter • Orbit: 384,000 km • Description: small, airless, cratered • surface is similar to Mercury

  7. Timeline of Moon Exploration • Luna 1 (USSR, 1959) first spacecraft to fly by the Moon • Luna 2 (USSR, 1959) • Luna 9 (USSR, 1966) first lunar lander • Luna 10 (USSR, 1966) • Apollo 8 (USA, 1968) first manned orbiter • Apollo 11 (USA, 1969) • Luna 16 (USSR), 1970) first automated sample return

  8. Near and Far Sides of the Moon

  9. Why is the Moon Airless? • Gravity • Thermal motions • All molecules have a velocity proportional to their temperature • The Moon has no atmosphere because this velocity is too large for its gravity to overcome

  10. The Surface of the Moon • Maria: • covered with dark colored mare basalt • similar to lava on Earth • Highlands: • covered with light colored anorthosite • very old (more than 4 billion years) • Moon rocks are similar in many ways to Earth rocks, but are depleted in volatiles

  11. Mare Basalt and Anorthosite

  12. Tycho and Rays

  13. Falling Bodies • Real impactors get their energy from their very high orbital velocities • A body dropped from a height has potential energy: PE = mgh • 1000 grams = 1 kg • g = 9.8 m/s2 • h is the height above the surface in meters

  14. Energy KE = ½mv2 • Where v is the velocity at impact in meters per second • The kinetic energy at impact must equal the potential energy at the drop point

  15. The Moon’s Interior • Moon is much less active than the Earth • Moon is much less dense than the Earth • Moon once had a magnetic field but does not today, indicating that the core has solidified

  16. Inside The Moon

  17. Moon Formation Theories

  18. Collisional Ejection Theory • The collision put large amounts of debris in orbit, which formed into the Moon • Energy from impact depleted the Moon in volatiles • The ejected material was mostly mantle rock, so the Moon has a very small core

  19. 4.6 billion years ago: 4.6-3.8 billion years ago: ~3.8 billion years ago: large impacts produce mare basins 3.8-3.1 billion years ago: 3 billion years ago-present core solidified, no more magnetic field small amounts of cratering A History of the Moon

  20. Next Time • Read Chapter 10

  21. Summary • Moon was formed 4.6 billion years ago when large impactor hit the Earth • Moon has a low density because it has only a small iron core • Moon has become tidally lock so that only the near-side faces Earth • Most of our information about the Moon comes from the Apollo missions

  22. Summary: Surface • Maria • large impacts produced basins which then filled with lava • darker, denser and younger than the highlands • Highlands • regions that have not experienced large impacts or lava • lighter, less dense and older than the Maria • Large numbers of impacts have covered the surface with craters and regolith (dust)

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