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    Ast1010 lecture 10 post Ast1010 lecture 10 post Presentation Transcript

    • 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!!!
    • Astronomy 1010 Introduction to Astronomy Lecture 10
    • Why does the moons appearance change?
    • 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.
    • 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.
    • 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
    • The Phases of the Moon Evening Sky
    • The Phases of the Moon Morning Sky
    • 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.
    • The dark side of the moon
      • Is there a dark side of the moon?
    • 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
    • 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.
    • Synodic vs Sidereal
      • Sidereal period = time for moon to complete one full orbit of the earth
      • Synodic period = time between successive New Moons.
    • Sidereal Period
      • The Moon orbits Earth in a sidereal period of 27.32 days.
      27.32 days Earth Moon Fixed direction in space
    • 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
    • The size of the moon
    • Lunar motions Inclination of the Moons orbit 5 o Ecliptic plane Moon ’ s Orbital Plane
    • Libration http://upload.wikimedia.org/wikipedia/commons/c/c0/Lunar_libration_with_phase2.gif
    •  
    • Earthrise from lunar orbit, Apollo 8 Earth rising, from Japan’s Kaguya spacecraft
    • Eclipses
    • 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?