Download The Moon: Size, Orbit, Phases, and Theories of Formation and more Slides Earth, Atmospheric, and Planetary Sciences in PDF only on Docsity! )
Earth and Moon
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http://solarsystem.nasa.gov/multimedia/gallery/Earth_Moon.jpg
Earth’s Moon What’s the Moon like? What do people see when they look at the Moon? http://photojournal.jpl.nasa.gov/catalog/PIA00094 Moon Size ~ 1/4 width of Earth Radius of 1080 miles Gravity ~1/6 of Earth’s http://grin.hq.nasa.gov/IMAGES/SMALL/GPN-2000-001444.jpg Relative Size and Distance of Earth and Moon? http://nix.ksc.nasa.gov/info;jsessionid=gfuzp418gewa?id=C-1979-00910&orgid=2 http://visibleearth.nasa.gov/view_rec.php?id=1624 Earth and Moon to Scale If Earth were a basketball, then the Moon would be a tennis ball, 23.5 feet away Moon’s Orbit Orbits (revolves around) Earth every 27.3 days Elliptical orbit (not a perfect circle) 360,000 km 406,000 km 224,000 miles 252,000 miles http://solarsystem.nasa.gov/multimedia/display.cfm?IM_ID=442 The Near Side The Moon rotates in 27.3 days. The Moon orbits Earth in 27.3 days. Because the Moon rotates and revolves at the same rate, we only see one side The NEAR side There is NO DARK SIDE There is a FAR side…. And the Backside! The FAR side http://photojournal.jpl.nasa.gov/catalog/PIA00304
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www.MrEclipse.com ©2000 F. Espenak
Moon Stats Moon’s orbit around Earth is inclined about 5 degrees to Earth’s plane of orbit around the Sun Ecliptic plane Sun Earth Moon Moon’s orbital plane Image created by LPI staff The Five Major Theories of Formation of the Earth’s Moon Did the moon form by Fission? • Theory proposed by Darwin • Based on fast-spinning primordial earth • Earth spun and flattened so quickly that it ejected a large piece of material, which eventually became the moon • Strengths: Isotopic ratio and Iron content similarities between Earth and Moon are explained • Flaws: Energy needed to cause loss of the material not supported by present day spinning of the earth The Capture Theory • Ring of dust around the earth slows the moon, which has already formed, allowing it to be captured into the earth’s gravitational field. Capture Theory Continued… • The Capture theory postulates that the moon was formed at another place and time in the solar system and while passing by the earth, it was pulled into the earth’s gravitational field. • Reasonable hypothesis because many moons surrounding other planets are actually captured asteroids and not objects that formed in place with the mother planet. A moon that is captured would most likely have a non-spherical shape. Ex. Phobos and Deimos, the moons of Mars The Colliding Planetesimals Theory • Hypothesizes that the moon condensed from the debris of planetesimaly sized objects that collided during the formation of the solar system • Limited evidence to support this theory. • Current lunar mission is studying this theory. The One that Works! The Collision-Ejection Theory aka: The Giant Impactor Theory What this theory is all about • hypothesizes that the moon was formed when a planetesimal the size of mars struck the earth, thereby ejected large volumes of matter from the earth. • disk of orbiting material ejected from the collision eventually condensed to form our moon in its orbit around the Earth. Why this theory works Explains the Lack of volatiles on the Moon’s surface • In order to explain the lack of volatiles on the moon, we would need an event which created a heat so high that all would have been vaporized. If an object the size of Mars were to collide with the forming Earth, the heat produced by this collision would provide a reasonable explanation as to why the moon’s surface characteristics imply that it has been ‘baked’ more than the earth.
