再見了,太陽
D: Wow! What a beautiful sunset.
Y: Enjoy it while it lasts, the sun won‘t 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: Won't that make things really cold down here?
Y: Actually, there won't 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. It’s 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 sun’s core to contract. When it contracts the core will get hotter, which will heat up the sun’s upper layers and make them expand. The sun will then become what’s called a red giant, and its radius will reach just past the orbit of Venus.
D: Which is bad for us.
Y: We’ll be burned to a crisp.
D: That's sounds painful.
Y: After a few billion years the core will begin to cool and expand. The sun’s 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, we’re pretty much doomed.
Y: Yes, but not for billions of years. Who knows? By then, human's might been living on another planet.
D: 哇!多么美麗的夕陽啊!
Y: 盡情欣賞吧,太陽不會(huì)永遠(yuǎn)存在的。
D: 你的意思是,有朝一日太陽會(huì)消失?
Y: 不是完全消失,太陽的能量最后會(huì)耗盡并枯竭。
D: 那樣的話,地球就會(huì)變得很冷了。
Y: 實(shí)際上,那時(shí)地球就不存在了。沒有了太陽,地球也將毀滅。
D: 等一下,你從頭開始說。
Y: 好的。像所有的行星一樣,太陽從根本上說,是一個(gè)巨型核反應(yīng)堆,通過燃燒氫氣產(chǎn)生能量。但是,就像任一反應(yīng)堆,太陽需要燃料來保持運(yùn)作。它已經(jīng)良好運(yùn)作大約45億年了,并且將會(huì)持續(xù)燃燒50億年左右。
D: 到那時(shí),燃料就會(huì)耗盡。
Y: 是的。當(dāng)太陽能量耗盡,地心引力會(huì)使得太陽核心縮小。縮小地同時(shí)溫度變得更得高,這樣就加劇了太陽外層的燃燒并使其膨脹。太陽就變成了所謂哦紅巨星,它的半徑將會(huì)達(dá)到以前金星的運(yùn)行軌道。
D: 那樣會(huì)對我們有害。
Y: 我們會(huì)被燒成土豆片的。
D: 聽起來很痛苦。
Y: 數(shù)十億年后太陽中心開始冷卻并擴(kuò)大。太陽的上層也將擴(kuò)大,失去物質(zhì)重量,最后中心冷卻到一定程度就成了白矮星,最終成黑矮星。
D: 那時(shí),我們就注定要完蛋了。
Y: 是的。但那是幾十億年以后的事了。誰知道呢?到那時(shí),人類也許已經(jīng)生活在另一個(gè)星球上了。