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Unformatted text preview: Astro 1 Section 1 Professor Brandt Wednesday April 21th 1999 Announcements: Lecture notes: Lecture 42. Earth's Moon Mean distance = 384000 km. Period relative to stars (sidereal) = 27.3 days. Period as seen from Earth (synodic) = 29.5 days. 1/4 radius of Earth = 1740 km. 1/80 mass of Earth = 7.35 E22 kg. A bit less dense than Earth = 3360 kg/m 3 When looking at Moon see dark and light patches. Lunar lowlands are smooth dark. Highlands are battered by craters. The flat dark plains of the lunar lowlands are known as maria = "seas" in Latin. Early in Moon's history large meteor impacts blasted out craters lava rose up from inside Moon to fill these somewhat leading to darkness and lack of craters (since cratering heavier early on). History of Earth's Moon . Dominant fact is that Moon is small size. When moon formed it was molten and heavy elements sank to the middle. (4.1- 4.5 billion years ago.) Today may be slightly molten in the middle but not too much....
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- Spring '99