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TPO3托福听力Lecture4原文文本
Spectroscopy
Professor: Now astronomy didn’t really bloom into the science it is today until the development of spectroscopy. Spectroscopy is basically the study of spectra and spectral lines of light, and specifically for us, the light from stars. It makes it possible to analyze the light emitted from stars. When you analyze this light, you can figure out their distance from the earth, and identify what they are made of, determine their chemical composition.
Before we get into that though, it’s probably a good thing to back up a bit. You all know how when you take a crystal prism and pass a beam of sunlight through it, you get a spectrum, which looks like a continuous band of rainbow colors. The light that we see with our human eyes as a band of rainbow color falls in a range of what’s called visible light. And visible light spectroscopy is probably the most important kind of spectroscopy. Anyone want to take a stab at the scientific term for visible light? And I’m sure all of you know this because you all did the reading for today.
Student: Optical radiation. But I thought being exposed to radiation is dangerous.
Professor: Yes, and no. If you are talking about radiation, like in the element Uranium, yeah, that’s dangerous. But radiation as a general term actually refers to anything that spreads away from its source. So optical radiation is just visible light energy spreading out.
OK, so we’ve got a spectrum of a beam of sunlight and it looks like the colors bleed into each other. There are no interruptions, just a band flowing from violet to green, to yellow, to… you get the idea. Well, what happens if the sunlight’s spectrum is magnified? Maybe you all didn’t do the reading. Well, here’s what you’d see. I want you to know this that this spectrum is interrupted by dark lines called spectral lines.
If you really magnify the spectrum of the sunlight, you could identify more than 100,000 of them. They may look like kind of randomly placed, but they actually form many distinct patterns. And if you were looking at the spectrum of some other star, the colors would be the same. But the spectral lines would break it up at different places, making different patterns. Each pattern stands for a distinct chemical element, and so different sets or patterns of spectral lines mean that the star has a different chemical composition.
Student: So how do we know which spectral patterns match up with which elements?
Professor: Well, a kind of spectroscopic library of elements was compiled using flame tests. A known element, say a piece of iron for example, is heated in a pure gas flame. The iron eventually heats to the point that it radiates light. This light is passed through a prism, which breaks it up into a spectrum. And a unique pattern, kind of like a chemical fingerprint of spectral lines for that element appears.
This process was repeated over and over again for many different elements, so we can figure out the chemical makeup of another star by comparing the spectral pattern it has to the pattern of the elements in the library. Oh, an interesting story about how one of the elements was discovered through spectroscopy. There was a pretty extensive library of spectral line patterns of elements even by the 1860s.
A British astronomer was analyzing a spectrograph of sunlight, and he noticed a particular pattern of spectral lines that didn’t match anything in the library. So he put two and two together, and decided there was an element in the sun that hadn’t been discovered here on the earth yet. Any guesses about what that element is? It actually turned out to be pretty common and I’m sure all of you know it. OK, let’s try something else. Any of you happened to be familiar with the Greek word for “sun” by chance?
Student: Something like “Helius” or something like that. Oh it must be “Helium”. So you are saying that Helium was discovered on the sun first.
Professor: Yes, and this is a good example of how important spectroscopy is in astronomy.
TPO3托福听力Lecture4题目文本
1.What is the lecture mainly about?
a) Different ways of magnifying the spectrum of a star
b) How a chemical element was first discovered on the Sun
c) How astronomers identify the chemical elements in a star
d) Why the spectra of different stars are composed of different colors
2.What does the professor explain to one of the students about the term “radiation”?
a) It is defined incorrectly in the textbooks.
b) It was first used in the nineteenth century.
c) It is rarely used by astronomers.
d) It does not refer only to harmful energy.
3.What can be inferred about two stars if their spectra have similar spectral line patterns?
a) The stars are approximately the same distance from the Earth.
b) The stars probably have some chemical elements in common.
c) The stars have nearly the same brightness.
d) The stars are probably of the same size.
4.According to the professor, what is the purpose of heating an element in a spectroscopic flame test?
a) To cause an element to emit light
b) To study an element in combination with other elements
c) To remove impurities from the element
d) To measure an element’s resistance to heat
5.Why does the professor say this?
a) He is about to provide some background information.
b) He is about to repeat what he just said.
c) He intends to focus on the history of astronomy.
d) He intends to explain two different points of view.
6.Why does the professor ask this?
a) To check the students’ understanding of their reading assignment
b) To give the students a hint to the answer to his previous question
c) To emphasize how important it is for astronomers to study Greek
d) To remind the students about the historical background of astronomy
TPO3托福听力Lecture4答案解析
第1题：主旨题
正确答案：C
对应原文：0'13"-0'36"Spectroscopy is basically the study of spectra and spectral lines of light, and specifically for us, the light from stars. It makes it possible to analyze the light emitted from stars. When you analyze this light, you can figure out their distance from the earth, and identify what they are made of, determine their chemical composition.
解析：开门见山。光谱学的发展推动了天文学的发展，通过对光谱的研究，我们能够分析从星体上发出来的光线，从而了解该星体离地球的距离，组成成分。
第2题：细节题
正确答案：D
对应原文：1'21"-1'41"Yes, and no. If you are talking about radiation, like in the element Uranium, yeah, that’s dangerous. But radiation as a general term actually refers to anything that spreads away from its source. So optical radiation is just visible light energy spreading out.
解析：学生认为暴露在辐射下很危险，但是光辐射分情况，像铀元素的辐射是危险的，但是光辐射是可见光源发出来的，所以不是危险的，由此可见，“辐射”不仅仅指危险的能量。
第3题：推断题
正确答案：B
对应原文：2'29"-2'46"But the spectral lines would break it up at different places, making different patterns. Each pattern stands for a distinct chemical element, and so different sets or patterns of spectral lines mean that the star has a different chemical composition.
解析：每一个星体的光谱线是由不同图案组成的，每一个图案代表着不同的化学元素，文中说，如果图案不同，意味着两个星体的化学成分不同，反过来推理，如果图案相同，则意味两个星体有着同样的化学组成。
第4题：目的题
正确答案：A
对应原文：2'56"-3'7"A known element, say a piece of iron for example, is heated in a pure gas flame. The iron eventually heats to the point that it radiates light.
解析：火焰测试的目的就是为了加热使一种元素发出光线，从而得到属于该元素的独一无二的光谱线图案，收集到光谱合集中。
第5题：重听-目的题
正确答案：A
对应原文：0'36"-0'41"Before we get into that though, it’s probably a good thing to back up a bit.
解析：从"back up"这个词组就可以明显知道，教授将要提供一些背景知识。
第6题：重听-目的题
正确答案：B
对应原文：4'14"-4'19"Any of you happened to be familiar with the Greek word for “sun” by chance?
解析：教授让同学们猜一下这个未知元素是什么，然后提出一个问题问谁碰巧知道希腊语中太阳这个单词，目的是为了给学生们先做，通过单词发音联想到Helium这个元素，从而知道未知元素是什么这个问题的答案。
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