lecture15spring2009

lecture15spring2009 - Astronomy 100 - Dr. Rhodes Lecture #...

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Unformatted text preview: Astronomy 100 - Dr. Rhodes Lecture # 15 - 2/20/2009 Chapter 6: The Earth-Moon System The Moons Surface The Moons surface can be divided into maria and mountainous, cratered regions. The maria (singular mare ) are any of the lowlands of the Moon or Mars that resemble a sea when viewed from Earth. The lunar maria were named this way by Galileo, who thought they were oceans. Most craters on the Moon are the result of impacts by meteorites an interplanetary chunk of matter that has struck a planet or moon. Four Stages in the Creation of an Impact Crater on the Moon Chapter 6: The Earth-Moon System The Moons Surface The Earth has few impact craters which are still visible because the atmosphere keeps all but the largest particles from reaching the surface. Over time, erosion and tectonic plate movement have erased all but a relative few of the largest craters. On the airless Moon, on Mercury, on the satellites of other planets, and even on the asteroids, the craters remain intact and visible for billions of years. Chapter 6: The Earth-Moon System The Moons Surface The Moons surface is covered with two different minerals, one of which is basalt . The lunar highlands are light in color, while the lunar maria are much darker in color. The crust of the Moon ranges in depth from 60 100 km and is thinner on the side facing the Earth than it is on the lunar far side. The mountains on the Moon are the result of extensive cratering over eons (i.e., they are not the result of tectonic activity there). Chapter 6: The Earth-Moon System The History of the Moon Radioactive dating techniques on the 840 pounds of Moon rocks brought back to Earth by the Apollo astronauts have been indispensable in forming a model of the Moons history. The Moon formed about 4.6 billion years ago. Most craters formed between 4.2 and 3.9 billion years ago. Giant impacts near the end of the cratering formed the maria as heated lava escaped from the lunar interior. Chapter 6: The Earth-Moon System The History of the Moon After the cratering ended, the Moons interior became hot for a second time due to radioactive decay and molten lava flowed. These flows ended about 3.1 billion years ago. The Moon has probably remained relatively unchanged since then. Micrometeorites (tiny meteorites) still hit the Moon, but no new crater has ever been observed to have been formed on the lunar surface since we have been studying it. Earths Surface Features Are Younger Than Are the Moons The Moons Surface Features Are Older Than the Earths Chapter 6: The Earth-Moon System...
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This note was uploaded on 03/03/2009 for the course ASTR 100 taught by Professor Rhodes during the Spring '08 term at USC.

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lecture15spring2009 - Astronomy 100 - Dr. Rhodes Lecture #...

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