再见了，太阳
D: Wow! What a beautiful sunset.
Y: Enjoy it while it lasts, the sun wont be around forever, you know.
D: You mean, one day the sun will disappear?
Y: Not exactly disappear, but the sun will eventually burn out and die.
D: Wont that make things really cold down here?
Y: Actually, there wont be any here, here. When the sun dies,the earth will be destroy too.
D: Wow, hold on, start from the beginning.
Y: Okay. Like all stars, the sun is basically a giant nuclear reactor that burns hydrogen to create energy. But like any reactor, the sun needs fuel to keep going. Its been going strong for around four|point|five billion years, and will probably keep burning for about five billion more.
D: But then, the fuel will run out?
Y: Exactly. When it does, gravity will cause the suns core to contract. When it contracts the core will get hotter, which will heat up the suns upper layers and make them expand. The sun will then become whats called a red giant, and its radius will reach just past the orbit of Venus.
D: Which is bad for us.
Y: Well be burned to a crisp.
D: Thats sounds painful.
Y: After a few billion years the core will begin to cool and expand. The suns upper layers will expand and lose material, and eventually the core will cool enough to become a white dwarf star, and finally a black dwarf.
D: So, were pretty much doomed.
Y: Yes, but not for billions of years. Who knows? By then, humans might been living on another planet.
D: 哇!多么漂亮的夕阳啊!
Y: 尽情赏析吧，太阳不会永远存在的。
D: 你的意思是，有朝1日太阳会消失?
Y: 不是完全消失，太阳的能量最后会耗尽并枯竭。
D: 那样的话，地球就会变得非常冷了。
Y: 事实上，那时地球就没有了。没了太阳，地球也将毁灭。
D: 等一下，你从头开始说。
Y: 好的。像所有些行星一样，太阳从根本上说，是一个巨型核反应堆，通过燃烧氢气产生能量。但，就像任一反应堆，太阳需要燃料来维持运作。它已经好运作大约45亿年了，并且将会持续燃烧50亿年左右。
D: 到那时，燃料就会耗尽。
Y: 是的。当太阳能量耗尽，地心引力会致使太阳核心缩小。缩小地同时温度变得更得高，如此就加剧了太阳外层的燃烧并使其膨胀。太阳就变成了所谓哦红巨星，它的半径将会达到以前金星的运行轨道。
D: 那样会对大家有害。
Y: 大家会被烧成土豆片的。
D: 听起来非常痛苦。
Y: 数十亿年后太阳中心开始冷却并扩大。太阳的上层也将扩大，失去物质重量，最后中心冷却到一定量就成了白矮星，最后成黑矮星。
D: 那时，大家就注定要完蛋了。
Y: 是的。但那是几十亿年未来的事了。哪个了解呢?到那时，人类或许已经生活在另一个星球上了。
