月球奥秘知多少？
<p>球俗称月亮，也称太阴。月球就是最明显的天然卫星的例子。在太阳系里，除水星和金星外，其他行星都是天然卫星。月球的年龄大约也是46亿年，它与地球形影相随，关系密切。月球也有壳、幔、核等分层结构。最外层的月壳平均厚度约为60-65公里。月壳下面到1000公里深度是月幔，它占了月球的大部分体积。月幔下面是月核，月核的温度约为1000度，很可能是熔融状态的。月球直径约3476公里，是地球的3/11。体积只有地球的1/49，质量约7350亿亿吨，相当于地球质量的1/81，月面的重力差不多相当于地球重力的1/6。月球上面有阴暗的部分和明亮的区域。早期的天文学家在观察月球时，以为发暗的地区都有海水覆盖，因此把它们称为“海”。着名的有云海、湿海、静海等。而明亮的部分是山脉，那里层峦叠嶂，山脉纵横，到处都是星罗棋布的环形山。位于南极附近的贝利环形山直径295公里，可以把整个海南岛装进去。最深的山是牛顿环形山，深达8788米。除了环形山，月面上也有普通的山脉。高山和深谷叠现，别有一番风光。</p><p><span word="The">The</span> <span word="ball">ball</span> <span word="is">is</span> <span word="commonly">commonly</span> <span word="known">known</span> <span word="as">as</span> <span word="the">the</span> <span word="moon">moon</span>, <span word="also">also</span> <span word="known">known</span> <span word="as">as</span> <span word="the">the</span> <span word="Taiyin">Taiyin</span>. <span word="The">The</span> <span word="moon">moon</span> <span word="is">is</span> <span word="the">the</span> <span word="most">most</span> <span word="obvious">obvious</span> <span word="example">example</span> <span word="of">of</span> <span word="a">a</span> <span word="natural">natural</span> <span word="satellite">satellite</span>. <span word="In">In</span> <span word="the">the</span> <span word="solar">solar</span> <span word="system">system</span>, <span word="except">except</span> <span word="for">for</span> <span word="mercury">mercury</span> <span word="and">and</span> <span word="Venus">Venus</span>, <span word="other">other</span> <span word="planets">planets</span> <span word="are">are</span> <span word="natural">natural</span> <span word="satellites">satellites</span>. <span word="The">The</span> <span word="moon">moon</span> <span word="is">is</span> <span word="also">also</span> <span word="about">about</span> 4.6 <span word="billion">billion</span> <span word="years">years</span> <span word="old">old</span>. <span word="It">It</span> <span word="is">is</span> <span word="closely">closely</span> <span word="related">related</span> <span word="to">to</span> <span word="the">the</span> <span word="earth">earth</span>. <span word="The">The</span> <span word="moon">moon</span> <span word="also">also</span> <span word="has">has</span> <span word="layers">layers</span> <span word="of">of</span> <span word="crust">crust</span>, <span word="mantle">mantle</span> <span word="and">and</span> <span word="core">core</span>. <span word="The">The</span> <span word="average">average</span> <span word="thickness">thickness</span> <span word="of">of</span> <span word="the">the</span> <span word="outermost">outermost</span> <span word="moon">moon</span> <span word="shell">shell</span> <span word="is">is</span> <span word="about">about</span> 60-65 <span word="km">km</span>. <span word="Below">Below</span> <span word="the">the</span> <span word="moon">moon</span>'<span word="s">s</span> <span word="crust">crust</span> <span word="to">to</span> <span word="a">a</span> <span word="depth">depth</span> <span word="of">of</span> 1000 <span word="kilometers">kilometers</span> <span word="is">is</span> <span word="the">the</span> <span word="moon">moon</span>'<span word="s">s</span> <span word="mantle">mantle</span>, <span word="which">which</span> <span word="accounts">accounts</span> <span word="for">for</span> <span word="most">most</span> <span word="of">of</span> <span word="the">the</span> <span word="moon">moon</span>'<span word="s">s</span> <span word="volume">volume</span>. <span word="Below">Below</span> <span word="the">the</span> <span word="mantle">mantle</span> <span word="is">is</span> <span word="the">the</span> <span word="lunar">lunar</span> <span word="core">core</span>, <span word="which">which</span> <span word="is">is</span> <span word="probably">probably</span> <span word="in">in</span> <span word="a">a</span> <span word="molten">molten</span> <span word="state">state</span> <span word="with">with</span> <span word="a">a</span> <span word="temperature">temperature</span> <span word="of">of</span> <span word="about">about</span> 1000 <span word="degrees">degrees</span>. <span word="The">The</span> <span word="diameter">diameter</span> <span word="of">of</span> <span word="the">the</span> <span word="moon">moon</span> <span word="is">is</span> <span word="about">about</span> 3476 <span word="kilometers">kilometers</span>, <span word="which">which</span> <span word="is">is</span> 3 / 11 <span word="of">of</span> <span word="the">the</span> <span word="Earth">Earth</span>'<span word="s">s</span>. <span word="Its">Its</span> <span word="volume">volume</span> <span word="is">is</span> <span word="only">only</span> 1 / 49 <span word="of">of</span> <span word="the">the</span> <span word="earth">earth</span>'<span word="s">s</span>, <span word="and">and</span> <span word="its">its</span> <span word="mass">mass</span> <span word="is">is</span> <span word="about">about</span> 735 <span word="billion">billion</span> <span word="tons">tons</span>, <span word="which">which</span> <span word="is">is</span> <span word="equivalent">equivalent</span> <span word="to">to</span> 1 / 81 <span word="of">of</span> <span word="the">the</span> <span word="earth">earth</span>'<span word="s">s</span> <span word="mass">mass</span>. <span word="The">The</span> <span word="gravity">gravity</span> <span word="of">of</span> <span word="the">the</span> <span word="moon">moon</span> <span word="is">is</span> <span word="about">about</span> 1 / 6 <span word="of">of</span> <span word="the">the</span> <span word="earth">earth</span>'<span word="s">s</span> <span word="gravity">gravity</span>. <span word="There">There</span> <span word="are">are</span> <span word="dark">dark</span> <span word="parts">parts</span> <span word="and">and</span> <span word="bright">bright</span> <span word="areas">areas</span> <span word="on">on</span> <span word="the">the</span> <span word="moon">moon</span>. <span word="When">When</span> <span word="early">early</span> <span word="astronomers">astronomers</span> <span word="looked">looked</span> <span word="at">at</span> <span word="the">the</span> <span word="moon">moon</span>, <span word="they">they</span> <span word="thought">thought</span> <span word="that">that</span> <span word="the">the</span> <span word="dark">dark</span> <span word="areas">areas</span> <span word="were">were</span> <span word="covered">covered</span> <span word="with">with</span> <span word="sea">sea</span> <span word="water">water</span>, <span word="so">so</span> <span word="they">they</span> <span word="called">called</span> <span word="them">them</span> "<span word="sea">sea</span>". <span word="Famous">Famous</span> <span word="are">are</span> <span word="the">the</span> <span word="sea">sea</span> <span word="of">of</span> <span word="clouds">clouds</span>, <span word="the">the</span> <span word="sea">sea</span> <span word="of">of</span> <span word="dampness">dampness</span>, <span word="the">the</span> <span word="sea">sea</span> <span word="of">of</span> <span word="tranquility">tranquility</span>, <span word="etc">etc</span>. <span word="And">And</span> <span word="the">the</span> <span word="bright">bright</span> <span word="part">part</span> <span word="is">is</span> <span word="the">the</span> <span word="mountains">mountains</span>, <span word="where">where</span> <span word="there">there</span> <span word="are">are</span> <span word="many">many</span> <span word="mountains">mountains</span> <span word="and">and</span> <span word="mountains">mountains</span>, <span word="and">and</span> <span word="there">there</span> <span word="are">are</span> <span word="many">many</span> <span word="ringed">ringed</span> <span word="mountains">mountains</span> <span word="everywhere">everywhere</span>. <span word="Bailey">Bailey</span> <span word="crater">crater</span>, <span word="located">located</span> <span word="near">near</span> <span word="the">the</span> <span word="south">south</span> <span word="pole">pole</span>, <span word="has">has</span> <span word="a">a</span> <span word="diameter">diameter</span> <span word="of">of</span> 295 <span word="kilometers">kilometers</span> <span word="and">and</span> <span word="can">can</span> <span word="accommodate">accommodate</span> <span word="the">the</span> <span word="whole">whole</span> <span word="Hainan">Hainan</span> <span word="Island">Island</span>. <span word="The">The</span> <span word="deepest">deepest</span> <span word="mountain">mountain</span> <span word="is">is</span> <span word="Newton">Newton</span> <span word="crater">crater</span>, <span word="which">which</span> <span word="is">is</span> 8788 <span word="meters">meters</span> <span word="deep">deep</span>. <span word="In">In</span> <span word="addition">addition</span> <span word="to">to</span> <span word="the">the</span> <span word="crater">crater</span>, <span word="there">there</span> <span word="are">are</span> <span word="ordinary">ordinary</span> <span word="mountains">mountains</span> <span word="on">on</span> <span word="the">the</span> <span word="moon">moon</span>. <span word="There">There</span> <span word="are">are</span> <span word="mountains">mountains</span> <span word="and">and</span> <span word="deep">deep</span> <span word="valleys">valleys</span>. <span word="There">There</span> <span word="is">is</span> <span word="no">no</span> <span word="other">other</span> <span word="scenery">scenery</span>.</p>
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