phys0001_chapter07

phys0001_chapter07 - Chapter 7 The Moon and Eclipses The...

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Chapter 7 The Moon and Eclipses The Moon The Moon is the Earth's only natural satellite. Its average distance from the Earth is 30 times the Earth's diameter. Its radius is only about one-fourth the Earth's and its mass is only 1/81 the mass of the Earth. There is no atmosphere on the Moon. (Actually, it is very very thin relative to the Earth's.) Here shows a picture of the full Moon. The dark areas are called maria (singular mare ), the seas. They are in fact the solidified lava flows, which occurred after the formation of the lunar crust. Most of the "hills" are craters , not volcanoes. The in-fall of massive objects onto the surface of the Moon creates those craters. The large number of craters on the Moon implies that there are very little lunar activities. In other words, the Moon is dead. The simple crater has a bowl shape. The complex crater has a small hill at the center, which was caused by the rebound of the material at the center. At the right is a close up. We can see both kinds of craters.
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The Moon is the only celestial object other than Earth that humans have visited. From the late 60s to the early 70s, U.S.A. had six crewed missions to the Moon, called the Apollo Missions. The time between successive new Moons, the synodic period , is 29.5 days. Interestingly, the rotational period of the Moon relative to the Sun is exactly the same as the synodic period. This matching is called the synchronous rotation
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phys0001_chapter07 - Chapter 7 The Moon and Eclipses The...

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