【英语时差8,16】地球为什么是圆的

 Don: It's time once again for one of those Moments of Science that we like to call "Never Thought to Ask."Our never thought to ask question for the day is: Why is the earth round?  Ya?l: Why is the earth round? I never thought to ask that.

D: Of course not!

Y: It just seems to be one of those things. The sun is round. The moon is round. The earth is round. What else would it be?

D: Why not a cube?

Y: A cube? No, that's silly.

D: Is it? Why?

Y: Because . . . because . . . (frustrated) . . . because really big things like to be round for some reason!

D: Exactly right. And that reason is gravity.

Y: Gravity?

D: Think of it this way. Suppose the earth were a cube. Then some points on its surface would be farther away from the center than others. The corners, for example, would be much farther out than the rest.

Y: I think I see where you're going. Since gravity works equally on everything, there would be a tendency to pull those uneven¹ places down. The surface would even itself out.

D: Right. And the only geometrical object in which every point on the surface is the same distance from the center is. . .?

Y: A sphere! . . . But wait a minute. I've seen pictures of asteroids³ that have all sorts of crazy shapes. Why aren't they round?

D: Only because they aren't big enough for gravity to be a determining factor. If that asteroid² were to suddenly become as big as a moon, it would indeed rearrange itself gradually into a sphere.

Y: Well, I never . . . ! 

1 uneven   

adj.不平坦的，不规则的，不均匀的

参考例句：

• The sidewalk is very uneven—be careful where you walk.这人行道凹凸不平—走路时请小心。
• The country was noted for its uneven distribution of land resources.这个国家以土地资源分布不均匀出名。

2 asteroid   

n.小行星；海盘车(动物)

参考例句：

• Astronomers have yet to witness an asteroid impact with another planet.天文学家还没有目击过小行星撞击其它行星。
• It's very unlikely that an asteroid will crash into Earth but the danger exists.小行星撞地球的可能性很小，但这样的危险还是存在的。

3 asteroids   

n.小行星( asteroid的名词复数 )；海盘车，海星

参考例句：

• Asteroids,also known as "minor planets",are numerous in the outer space. 小行星，亦称为“小型行星”，在外太空中不计其数。
• Most stars probably have their quota of planets, meteorids, comets, and asteroids. 多数恒星也许还拥有若干行星、流星、彗星和小行星。