【文摘】再见，太阳！

Have you ever considered the possibility that the sun will eventually burn out? Don and Yael discuss that sobering thought on this Moment of Science.  

[OUTSIDE INSECT SOUNDS]

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 destroyed too.

D: Whoa, hold on. Start from the beginning.

Y: Ok. Like all stars the sun is basically a giant nuclear reactor¹ 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. And 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 radius² will reach just past the orbit of Venus.

D: Which is bad for us.

Y: We'll be burned to a crisp.

D: That 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 dwarf³ star, and finally a black dwarf.

D: So we're pretty much doomed⁴.

Y: Yes, but not for billions of years. Who knows? By then humans might be living on another planet.

D: Or we'll have been enslaved by a bunch of dirty apes!

Y: I think someone's been watching too much cable TV.

1 reactor   

n.反应器；反应堆

参考例句：

• The atomic reactor generates enormous amounts of thermal energy.原子反应堆发出大量的热能。
• Inside the reactor the large molecules are cracked into smaller molecules.在反应堆里，大分子裂变为小分子。

2 radius   

n.半径，半径范围；有效航程，范围，界限

参考例句：

• He has visited every shop within a radius of two miles.周围两英里以内的店铺他都去过。
• We are measuring the radius of the circle.我们正在测量圆的半径。

3 dwarf   

n.矮子，侏儒，矮小的动植物；vt.使…矮小

参考例句：

• The dwarf's long arms were not proportional to his height.那侏儒的长臂与他的身高不成比例。
• The dwarf shrugged his shoulders and shook his head. 矮子耸耸肩膀，摇摇头。

4 doomed   

命定的

参考例句：

• The court doomed the accused to a long term of imprisonment. 法庭判处被告长期监禁。
• A country ruled by an iron hand is doomed to suffer. 被铁腕人物统治的国家定会遭受不幸的。