煎蛋小学堂:英语百科(视频+中英字幕) 第1课:夜空为什么是黑的
<p><span word="Why">Why</span> <span word="is">is</span> <span word="the">the</span> <span word="sky">sky</span> <span word="dark">dark</span> <span word="at">at</span> <span word="night">night</span>?夜空为什么是黑的？</p><p><span word="You">You</span> <span word="might">might</span> <span word="think">think</span> <span word="the">the</span> <span word="answer">answer</span> <span word="is">is</span> <span word="obvious">obvious</span> - <span word="the">the</span> <span word="sun">sun</span> <span word="isnt">isnt</span> <span word="up">up</span>! <span word="But">But</span> <span word="the">the</span> <span word="only">only</span> <span word="reason">reason</span> <span word="the">the</span> <span word="sky">sky</span> <span word="looks">looks</span> <span word="blue">blue</span> <span word="during">during</span> <span word="the">the</span> <span word="day">day</span> <span word="is">is</span> <span word="that">that</span> <span word="sunlight">sunlight</span> <span word="scatters">scatters</span> <span word="off">off</span> <span word="of">of</span> <span word="the">the</span> <span word="atmosphere">atmosphere</span> - <span word="if">if</span> <span word="we">we</span> <span word="didnt">didnt</span> <span word="have">have</span> <span word="an">an</span> <span word="atmosphere">atmosphere</span> (<span word="like">like</span> <span word="on">on</span> <span word="the">the</span> <span word="moon">moon</span>), <span word="the">the</span> <span word="sky">sky</span> <span word="would">would</span> <span word="always">always</span> <span word="be">be</span> <span word="dark">dark</span>, <span word="even">even</span> <span word="when">when</span> <span word="the">the</span> <span word="sun">sun</span> <span word="is">is</span> <span word="shining">shining</span>. <span word="So">So</span> <span word="lets">lets</span> <span word="rephrase">rephrase</span> <span word="the">the</span> <span word="question">question</span> - <span word="why">why</span> <span word="is">is</span> <span word="space">space</span> <span word="dark">dark</span>?你可能认为答案很简单——因为没有太阳嘛！但白天的天空之所以是蓝色的，完全因为大气层把阳光散射了。而如果没有大气层，就比如月球，那么天空就一直都是黑的，即便有太阳照射，那就让我们换种问法——为什么太空是黑色的？</p>太空里充满了各种各样的恒星，每一颗的亮度都和太阳一样，而在无穷无尽的宇宙中，不管你选择任何一个方向，只要你走得足够远，你都能遇到一颗恒星，或者一个星系，于是天空就应该是亮如白昼的，不论白天还是黑夜。<span word="And">And</span> <span word="since">since</span> <span word="its">its</span> <span word="not">not</span>, <span word="does">does</span> <span word="the">the</span> <span word="darkness">darkness</span> <span word="of">of</span> <span word="the">the</span> <span word="night">night</span> <span word="sky">sky</span> <span word="mean">mean</span> <span word="that">that</span> <span word="theres">theres</span> <span word="some">some</span> <span word="distance">distance</span> <span word="away">away</span> <span word="from">from</span> <span word="us">us</span> <span word="when">when</span> <span word="stars">stars</span> <span word="and">and</span> <span word="galaxies">galaxies</span> <span word="just">just</span>… <span word="stop">stop</span>? <span word="A">A</span> <span word="boundary">boundary</span> <span word="between">between</span> <span word="something">something</span> <span word="and">and</span> <span word="nothing">nothing</span>?但是事实却并非如此，那么，黑色的夜空是否告诉了我们，在一定的距离以外，就没有恒星或者星系了吗？是不是存在一个有星星和没有星星的边界？</p>
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