英语听力文摘流星与地球运动

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The Front End of the Earth

火流星看上去非常明亮，像条闪闪发光的巨大火龙，发着“沙沙”的响声，有时还有爆炸声。有的火流星甚至在白天也能看到。火流星的出现是因为它的流星体质量较大(质量大于几百克)，进入地球大气后来不及在高空燃尽而继续闯入稠密的低层大气，以极高的速度和地球大气剧烈摩擦，产生出耀眼的光亮，并且通常会在空中走出“S”型路径。火流星消失后，在它穿过的路径上，会留下云雾状的长带，称为“流星余迹”;有些余迹消失得很快，有的则可存在几秒钟到几分钟，甚至长达几十分钟。

Enjoy star gazing?Then this Moment of Science is for you!

On a previous show we mentioned how not all shooting stars(流星) have the same speed. Some disappear almost immediately, while others make a nice slow line across the sky.

If you enjoy watching the slow ones, there is a way of upping your chances of seeing them. Go out just after sunset.That's because the slowest meteors come in the evening and the fastest ones come in the morning, just before sunrise.

Can you guess why?The speeds of meteors we see are increased or decreased by the earth’s motion. If we (1)charge into them (2)head-on our speed is added to their speed. If, on the other hand, we are moving away from them, our speed is (3)subtracted from their speed.

Now imagine yourself standing at the north pole, facing the direction the earth is moving through space. You rise up magically, far enough away that you can see the whole planet rotating underneath you while you yourself remain stationary. Which direction is it turning? Counterclockwise. Where is the sunlight? From your perspective, it’s on the left side of the planet.

That means that the front of the planet, or the part that’s charging into oncoming meteors, is the place where morning is beginning for people on earth. The back of the planet, meaning the part that’s moving away from meteors, is where evening is beginning.

It may seem funny, but every morning when you look up into the sky, you are looking in the same direction as the planet is moving. In the evening you are looking the other way. And the speed of shooting stars confirms it!

译文：

流星与地球运动

前面的文章中我们提到为什么不是所有流星都有相同的速度。有些几乎立即就消失了，而有些拖着长长的尾巴穿过天空。

如果你喜欢观看缓慢的流星，那么有一种方法可以增加你看到它们的几率。日落后就出门。最慢的流星在夜晚出现，最快的流星出现在早晨，就在太阳升起之前。

你猜猜为什么呢?我们看到的流星的运动速度随着地球的运动情况而增减。如果地球正对着流星的方向运动，那么我们的运速就会增加至它的运动速度中，反之，如果我们背向它们运动，那么它们的运速中就会减去地球运速这一部分。

现在想想你自己站在北极，面向地球穿过空间移动的方向。你奇迹般地上升，远到可以看到整个地球在你的脚下转动，而你自己保持静止。它是在向哪个方向运动呢?逆时针。太阳光在哪里呢?从你的角度来看，在地球的左侧。

这意味着在地球的前端，或者是在正对流星运动的地方，就是早晨的开始。地球的背面，也就是背向流星运动的地方，就是夜晚的开始。

这似乎非常有趣，但是每天早晨当你仰望天空时，你就是望着与地球转动相同的方向。晚上，你就是望着相反的方向。流星的速度证实了这一点。

Notes:

(1)charge into 冲进;撞上：

The students charged into the classroom to greet their teacher.

学生们冲进教室，向老师问好。