moon_and_mercury - The Moon Mass = 7.4 x 1025 g = 0.012...

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9/23/11 1 The Moon = 3.3 g/cm 3 (Earth 5.5 g/cm 3 ) = 1/6 that of Earth Mass Radius Density Gravity = 7.4 x 10 25 g = 0.012 M Earth = 1738 km = 0.27 R Earth This means: period of orbit = period of spin Why? Tidal Locking Earth The tidal bulge in the solid Moon elongates it slightly (2-3 km) along an axis pointing to Earth. Top view of Moon orbiting Earth If orbit period faster than spin period, tidal bulge would have to move around surface of Moon, creating friction, which slows the Moon’s spin down until tidal bulge no longer migrates around. We always see the same face of the Moon. Dark side of the moon Tides A feature of oceans (but solid material has small tides too). Two high and two low tides per day. Tides are due to Moon's gravitational pull being stronger on side of Earth closest to it (Sun causes smaller tides). Earth-Moon gravity keeps them orbiting each other. But side of Earth closest to Moon has slightly stronger pull to Moon => bulges towards it. Other side has weaker pull => bulges away compared to rest of Earth. The Earth spins once a day while the bulge always points towards and away from the Moon => high and low tides.
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9/23/11 2 Tides Tides The Lunar Surface - Large, dark featureless areas: "maria" or "seas". - Lighter areas at higher elevation: "highlands". maria highlands - Loads of craters (due mostly to meteorite impacts). No winds to erode them away. - Highlands have 10x the crater density of maria. Lunar Volcanism (long ago) Evidence: - Maria: result of old, widespread lava flows (filled in largest, early impact craters) The image can ot be displayed. Your computer may not have enough memory to open the image, or the image may have be n cor upted. Restart your computer, and then open the fle again. IF the red x stil ap ears, you may have to delete the image and then insert it again. - Linear chains of craters (not formed by impacts), probably marks ancient fault, collapsed lava domes - "Rilles": ditches indicating old lava flows Remember: volcanism is a way of losing internal heat Cratering - Impact speeds several km/sec - "Ejecta blanket" of pulverized rock surrounds crater
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moon_and_mercury - The Moon Mass = 7.4 x 1025 g = 0.012...

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