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地球的前端

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小编摘要:如果你喜欢观看飞的较慢的流星,有一种方法可以增大你看到他们的几率。那就是在日落之后观看。那是因为飞的最慢的流星出现在夜晚,而飞得最快的流星出现在早晨,而且恰恰是太阳还未升起的时候。你能猜到个中缘由吗?

The Front End of the Earth
地球的前端



On a previous show we mentioned how not all shooting stars 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 charge into them head-on our speed is added to their speed. If, on the other hand, we are moving away from them, our speed is 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!


在上一期节目中我们提到流星飞行速度是如何不完全一致的。一些流星几乎瞬间在视线中消失了,而其他流星却可以慢慢在天空中划出一道优美的弧线。

如果你喜欢观看飞的较慢的流星,有一种方法可以增大你看到他们的几率。那就是在日落之后观看。那是因为飞的最慢的流星出现在夜晚,而飞得最快的流星出现在早晨,而且恰恰是太阳还未升起的时候。你能猜到个中缘由吗?

流星速度的快慢取决于地球的运动,一方面如果地球与流星同向运动,那么流星的速度就是地球速度和它固有速度的加和。另一方面,如果地球同流星反向运行,地球就会离他们越来越远,流星速度就是要在原有速度上减去地球的速度。

现在,假设你站在北极,面朝地球在宇宙中运动的方向,然后神奇地飘了起来,飘到了足以看到整个地球在你脚下自转的高空,而你自己保持不动。地球在沿什么方向转动呢?答案是逆时针。那么阳光来自哪里呢?从你的角度来看,阳光是来自地球左侧的。

这意味着地球的前方,或者说地球将要迎接即将陨落的流星的那一面,就是对于在地球上的人们早晨开始的地方。而地球的背面,也就是与流星飞行方向相背的地区就是夜晚开始的地方。

这或许看起来有些好笑,但是,每天早晨当你抬头仰望天空的时候,你就正看向地球运动的方向。而在晚上你看到的却是与地球运动方向相反的方向。流星飞行的速度证明了这一点。

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2012-02-27 20:05 编辑:pliny
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