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托福TPO-26 Lecture 4(下)

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So the comet should be long gone by now, right?

所以,这颗彗星理应早就消失了,对吧?

I mean, how come Halley's is still there?

我是说,哈雷彗星怎么会还在这儿呢?

After four and a half billion years, how could it be?

在四十五亿年后,怎么可能还在呢?

Well, the answer is that this comet hasn't always been in such a short periodic orbit, since once a comet gets into an orbit that keeps it coming in close to the sun quite frequently...well, that comet's probably not going to be around too much longer.

答案是,这颗彗星不总是绕这个短周期性轨道运转,因为一旦彗星频繁进入了这种会使自己接近太阳的轨道,那彗星可能不久之后就不复存在了。

哈雷彗星2.jpg

So this kind of periodic orbit is only a phase in a comet's life.

所以这种周期性轨道只是彗星生命中的一个阶段。

A phase that just precedes its final breakup.

这个阶段预告它的最终解体。

We've seen comet do that, going toward the sun and come back around, torn into pieces.

我们已经见过彗星这么做了,靠近太阳,回来的时候已经碎了好多块了。

But lots of comet aren't like that.

但很多彗星不是这样的。

They come in, pass behind the sun, and then travel back out.

它们靠近太阳,从太阳后面经过,然后再离开。

But with an orbit so large, and its farthest place so far away from the sun that we just don't know how far out it goes.

但对于轨道范围这么大,轨道最远处离太阳这么远的彗星,我们不知道最远能到哪里。

We just can't determine that very accurately from the close, in part of the orbit that we do see.

我们在它(离我们)较近时,即它在我们可见范围的部分轨道内时,我们也无法决定。

So these are often called parabolic-orbit comet.

这种通常称为抛物线轨道彗星。

Parabolic means the orbit is open at the far end.

抛物线是指轨道远端是开放的。

Actually the orbit probably does close and return the comet to the vicinity of the sun eventually, but the period might be tens of thousands of years.

事实上,很可能轨道是封闭的,彗星最终会回到太阳附近,但这个周期可能需要上万年。

And basically, we can't determine it.

基本上我们是无法确定的。

So we just, we refer to them as open-end parabolic-orbit comets.

所以我们称之为开放性抛物线轨道彗星。

So, what can change a comet with one of these long orbit where they only come by the sun occasionally into a much more frequent periodic visitor?

那么,是什么改变了彗星,使其沿偶尔才会经过太阳的长轨道运行,变为更频繁的周期性拜访太阳?

Well, gravitational interaction with planets, right?

行星间的相互引力作用,对吧?

If a comet on one of these long period orbits at some point comet close to Jupiter or Saturn or one of the other planets, then the pull of that planet's gravity might alter the orbit, maybe make it much shorter.

假如,一颗沿这种长周期轨道运行的彗星在某个时候靠近木星或土星或别的行星,这些行星的引力可能会改变彗星的轨道,可能会让轨道变短。

So this comet, if it happens to pass by a planet just the right way, it can be drawn into a new orbit, one that will capture it and keep it coming back around the sun much more often.

如果这颗彗星恰好以正确的方式经过了一颗行星,彗星可被吸引到一个新的轨道上去,这个轨道会捕捉这颗彗星,让它更频繁地回到太阳附近。

重点单词   查看全部解释    
accurately ['ækjuritli]

想一想再看

adj. 准确地
adv. 精确地,准确地

 
frequent ['fri:kwənt]

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adj. 经常的,频繁的
vt. 常到,常去

 
periodic [.piəri'ɔdik]

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adj. 周期的,定期的,间歇的,完句的

 
alter ['ɔ:ltə]

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v. 改变,更改,阉割,切除

联想记忆
planet ['plænit]

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n. 行星

 
comet ['kɔmit]

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n. 慧星

 
interaction [.intə'rækʃən]

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n. 相互作用,相互影响,互动交流

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gravitational ['grævə'teiʃənəl]

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adj. 重力的,引力作用的

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eventually [i'ventjuəli]

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adv. 终于,最后

 
gravity ['græviti]

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n. 重力,严重,庄重,严肃

联想记忆

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