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Ast1010 lecture 10 post

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  • 1. Student Astronomical Society First Meeting!!!!! Wednesday, September 14 7:00 PM 5 th Floor of the Physics Building There will be refreshments!!! Student Astronomical Society First Meeting!!!!! Wednesday, September 14 Wednesday, September 14 Wednesday, September 14 7:00 PM 5 th Floor of the Physics Building There will be refreshments!!! 7:00 PM 5 th Floor of the Physics Building There will be refreshments!!! 7:00 PM 5 th Floor of the Physics Building There will be refreshments!!!
  • 2. Astronomy 1010 Introduction to Astronomy Lecture 10
  • 3. Why does the moons appearance change?
  • 4. Why do we see different phases of the Moon?
    • The motion of the Moon in its orbit around the Earth causes us to see different amounts of the Earth's shadow falling on the Moon.
    • The motion of the Moon in its orbit around the Earth causes us to see different amounts of the sunlit side of the Moon.
    • The distance of the Moon from the Earth changes because of the elliptical orbit of the Moon, causing the sunlit side of the Moon to move relative to the Earth.
    • The rotation of the Moon around its own axis causes us to see different amounts of the sunlit side of the Moon.
  • 5. The Phases of the Moon From Earth, we see different portions of the Moon’s surface lit by the sun, causing the phases of the moon.
  • 6. U.S. Naval Observatory Astronomical Applications Department Sun or Moon Rise/Set Table for One Year Sky Gazer Program – Explore, Phases of the Planets, Phases of the Moon Moon Phases http://www.valdosta.edu/~cbarnbau / astro_demos/frameset_moon.html
  • 7. The Phases of the Moon Evening Sky
  • 8. The Phases of the Moon Morning Sky
  • 9. Suppose that on a given evening you notice that the Moon has a crescent shape. This simple observation tells you
    • that at that particular time the Moon is closer to the Sun than you are.
    • that at that particular time the Moon is farther from the Sun than you are.
    • that the line from you to the Moon is exactly at right angles to the line from you to the Sun.
    • nothing at all about where the Moon is in space compared to you and the Sun.
  • 10. The dark side of the moon
    • Is there a dark side of the moon?
  • 11. Is there a dark side to the moon? Earth exerts tidal forces on the moon’s rocky interior -> It is rotating with the same period around its axis as it is orbiting Earth (tidally locked) -> We always see the same side of the moon facing Earth
  • 12. The Moon is seen to keep one face toward Earth at all times. If viewed from a point directly above the plane of the planetary system, how does it have to rotate to maintain this alignment? Q?
    • It must rotate once per year as Earth and Moon orbit the Sun together.
    • It must rotate once per day.
    • It must not rotate at all, since we always see the same face from Earth.
    • It must rotate once per month, or once per orbit around Earth.
  • 13. Synodic vs Sidereal
    • Sidereal period = time for moon to complete one full orbit of the earth
    • Synodic period = time between successive New Moons.
  • 14. Sidereal Period
    • The Moon orbits Earth in a sidereal period of 27.32 days.
    27.32 days Earth Moon Fixed direction in space
  • 15. Synodic Period
    • The Moon’s synodic period (to reach the same position relative to the sun) is 29.53 days (~ 1 month).
    Fixed direction in space Earth Moon Earth orbits around Sun => Direction toward Sun changes! 29.53 days
  • 16. The size of the moon
  • 17. Lunar motions Inclination of the Moons orbit 5 o Ecliptic plane Moon ’ s Orbital Plane
  • 18. Libration http://upload.wikimedia.org/wikipedia/commons/c/c0/Lunar_libration_with_phase2.gif
  • 19.  
  • 20. Earthrise from lunar orbit, Apollo 8 Earth rising, from Japan’s Kaguya spacecraft
  • 21. Eclipses
  • 22. Eclipses
    • Eclipses are shadows
    • If the earth is directly between the moon and the sun  lunar eclipse  the moon is in the Earth ’s shadow
    • If the moon is directly between the earth and the sun  solar eclipse  the earth is in the moon ’s shadow
    • Why don ’t we have an eclipse every month?