听力文摘：地球为什么是圆的？

Why the Earth Is Round?

地球为什么是圆的？

Our never-thought to ask question for today is: Why is the earth round? Why not a cube? A cube? No, that's silly. Is it? Why?

今天，我们“从未想过的问题”是：地球为什么是圆的？为什么不是方形的？方形？那太可笑了。是吗？为什么？

Because..., because really big things like to be round for some reason. Exactly right.And that reason is gravity.

因为……因为非常大的东西通常都是圆的。完全正确。这个原因就是重力。

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.

我们这样想，假设地球是一个立方体。而地球表面的某些端点离中间或其它端点比较远。比如，立方体的各个角离得很远。

Since gravity works equally on everything, there would be a tendency to pull those uneven¹ places down. The surface would even itself out. The only geometrical object in which every point on the surface is the same distance from the center is a sphere.

由于重力对所有物质的作用是相等的，因此不均匀的地方会被向下拉。表面使其本身变得平均。唯一一个表面上的每个角到中心距离都相等的几何物体就是球体。

But wait a minute, I've seen pictures of asteroids³ that have all sorts of crazy shapes. Why aren't they round? Only because they aren't big enough for gravity to be a determining factor. If an asteroid² were to suddenly become as big as a moon, it would indeed rearrange itself gradually into a sphere.

等一下，我看过很多行星的图片，它们都是奇形怪状的。它们为什么不是圆的？那只是因为行星太小，重力不能成为其决定因素。如果行星突然变得和月亮一样大，它就会真正重新安排逐渐变成一个球体。

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。