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托福TPO-13 Lecture 4

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Narrator:Listen to part of a lecture in an astronomy class.

独白:听下面一段天文学课上的演讲。
Professor:OK, I wanna go over the different types of meteoroids, and what we've learned from them about the formation of earth, and solar system.
教授:好的,我要讲一下各种不同的流星体,以及我们从这些流星体上获取的关于地球构造和太阳系的信息。
Uh… the thing is what's especially interesting about meteoroids is that they come from interplanetary space, but they consist of the same chemical elements that are in matter originated on earth, just in different proportions.
额,流星体特别有趣的一点是,这些流星体来自行星际空间,但是他们包含着同样的化学元素,这些物质来源于地球,只是成分所占比例不同而已。
But that makes it easier to identify something as a meteoroid, as it opposed to…to just a terrestrial rock.
但正因为如此人们可以更容易辨认出流星体,而不会将其当做一种地球上的岩石。
So to talk about where meteoroids come from, we need to talk about comets and asteroids, which basically...they're basically made up of debris left over from the origin of the solar system 4.6 billion years ago.
那么讲到流星体从何而来,我们就需要讨论下彗星和小行星,基本上说,这些流星体是由 46 亿年前太阳系诞生以来留下的废墟组成的。
Now I'm going a bit out of a boarder here…umm…I'm not going to go into any depth on the comets and asteroids now, but we'll come back later and do that.
现在,我要讲一下题外话,嗯,我现在不会详细深入讲彗星或小行星,我们以后再深入讲解。
From now, I'll just cover some basic info about them.
从现在开始,我会只讲一些基本信息。
OK, comets and asteroids.
好的,彗星和小行星。
It might help if you think of...remember we talked about the two classes of planets in our solar system?
这可能会对你们有所帮助,如果你想到……记得我们说过太阳系中的两类行星吗?
And how they differ in composition?
还有他们在成分上有什么不同的?
The terrestrial planets--like Mars and Earth--composed largely of rocks and metals, and the large gas giants, like Jupiter.
类地行星,像火星或地球,大部分是由岩石和金属构成的。另一种就像木星这种大行星,其星体上布满气体。
Well, the solar system also has two analogous classes of objects, smaller than planets--namely, asteroids and comets.
嗯,太阳系中还有两种相类似的星体分类,比行星要小,那就是小行星和彗星。
Relatively near the sun and inner solar system, between Jupiter and Mars to be precise, we've got the asteroid belt, which contains about 90 percents of all asteroids orbiting the sun.
相对而言,这些星体更接近太阳和太阳系内部,确切地说,处于木星和火星之间。我们知道小行星带的存在,这里面有 90%的小行星是绕着太阳而旋转的。
These asteroids are…uh…like the terrestrial planets, and they're composed mostly of rocky materials and metals.
这些小行星,额,就像是类地行星。他们主要是由岩石材料和金属构成的。
Far from the sun, in the outer solar system, beyond Jupiter's orbit, temperatures are low enough to permit ices to form out of water and…and out of gases like methane and carbon dioxide.
在远离太阳的地方,在太阳系外延,木星轨道之外,那里的气温很低,足以使某些水分凝结成冰,而且,释放出像甲烷和二氧化碳这样的气体。
Loose collections of these ices and small rocky particles form into comets.
这些冰块和小型的岩石微粒会集合起来,形成彗星。
So comets are similar in composition to the gas giants.
所以彗星的成分和气体巨星的成分是相类似的。
Both comets and asteroids are...typically are smaller than planets.
彗星和小行星都要比行星小很多。
And even smaller type of interplanetary debris is the meteoroid.
而甚至是更为小型的行星间的碎片也是行星体。
And it's from meteoroids that we get meteors and meteorites.
而从这些行星体中会有流星和陨石。
"Roids" are, for the most part anyway, they are just smaller bits of asteroids and comets.
“Roids”通常上讲,只是小行星和彗星的小型碎片。
When these bits enter earth's atmosphere, well, that makes them so special that they get a special name.
当这些碎片进入地球大气层之后,它们便会变得很特别,会有一个特别的名字,
They're called meteors.
它们被称为流星。
Most of them are very small, and they burn up soon after entering earth's atmosphere.
大部分流星都体积很小,在进入大气层之后会很快燃烧起来。
The larger ones that make it through the atmosphere and hit the ground are called meteorites.
那些体积较大,进入大气层之后直击地面的流星便叫做陨石。
So meteorites are the ones that actually make it through.
因此陨石其实就是那些穿透大气层到达地球表面的行星体。
Now we've been finding meteorites on earth for thousands of years, and we've analyzed enough of them to learn a lot about their composition, most come from asteroids, though a few may have come from comets.
如今我们发现陨石的历史已经有几千年了,我们已经对其进行了足够的分析,解了很多关于陨石的成分,知道大部分是来自小行星,尽管有些陨石是来自彗星。
So essentially they are rocks, and like rocks, they're mixtures of minerals.
所以,基本上讲,这些陨石就是岩石。它们是各种矿物的混合物。
They are generally classified into three broad categories--stones, stony irons and irons.
基本上被分为三大类:石头,陨铁石和铁块。
Stone meteoroids, which we refer to simply as, uh, stones, are almost entirely rock material.
某些行星体,我们简单称为,额,石头,基本上全部是岩石材料。
They actually account for almost all of the meteorite material that falls to earth.
事实上它们几乎占到所有落到地球表面陨石材料的全部。
But even so, it's rare to ever find one.
但即便如此,找到颗陨石都难。
I mean, it's easier to find an iron meteorite or stony iron.
我是说,找到一块铁陨星或陨铁石会更容易点。
Anyone guess why? Look at their names.
有人知道为什么吗?看看这些名字,
What do you think iron meteorites consist of?
你们觉得陨铁石包括什么呢?
Student:Mostly iron?
学生:大部分是铁吧?
Professor:Yeah… iron and some nickel, both of which are metals.
教授:是的,铁和镍,两者都是金属成分,
And, if you're trying to find metal?
而如果你正试图找某些金属材料的话?
Student:Oh! Metal detectors!
学生:哦!金属探测器!
Professor:Right, thank you.
教授:好的,谢谢。
At least that's part of it.
至少这是其中的一部分。
Stone meteoroids, if they lie around exposed to the weather for a few years, well, they're made of rock, so they end up looking almost indistinguishable from common terrestrial rocks-once that originated on earth.
如果暴露在某种天气中几年,嗯,由于他们都是由石头构成的,所以基本上这些石陨石跟那些普通的地球上的石头并无两样。
So it's hard to spot them by eye.
而要靠肉眼来察觉这些星体是比较难的。
But we can use metal detectors to help us find the others, and they're easier to spot by eye.
但是我们能用金属测探器帮助我们找到其他流星体,这些能更容易通过肉眼看到。
So most of the meteorites in collections, uh, in museums, they'll be...they're iron meteorites, or the stony iron kind, even though they only make up about 5percents of the meteorite material on the ground.
因此大部分聚合起来的陨石,额,在博物馆中的,它们将会,它们是铁陨星,或是陨铁石,即便这些星体只占到地面上的陨星材料的 5%。

重点单词   查看全部解释    
analogous [ə'næləgəs]

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adj. 类似的

 
composed [kəm'pəuzd]

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adj. 镇静的,沉着的

联想记忆
exposed [iks'pəuzd]

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adj. 暴露的,无掩蔽的,暴露于风雨中的 v. 暴露,

 
composition [.kɔmpə'ziʃən]

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n. 作文,著作,组织,合成物,成份

联想记忆
precise [pri'sais]

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adj. 精确的,准确的,严格的,恰好的

联想记忆
rocky ['rɔki]

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adj. 岩石的,像岩石的,坚硬的,麻木的,困难重重的

 
opposed [ə'pəuzd]

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adj. 反对的,敌对的 v. 和 ... 起冲突,反抗

 
permit ['pə:mit,pə'mit]

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n. 许可证,执照
v. 允许,许可

联想记忆
essentially [i'senʃəli]

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adv. 本质上,本来

 
rare [rɛə]

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adj. 稀罕的,稀薄的,罕见的,珍贵的
ad

 

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