托福模拟试题听力 - TPO19 - 讲座2

时间 : 2013-08-05 09:52来源 : VOA官网 收听下载次数 :
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TPO 19 Lecture 2 Astronomy 

Professor:So how many of you have seen the Milky Way, the Milky Galaxy in the sky? You, you have?

Student:Yeah, I was camping, and there was no moon that night, it was super dark.

Professor:Anybody else? Not too many. Isn’t that strange that the Milky Way is the galaxy that the planet earth is in, and most of us have never seen it? Now, what’s the problem here?

Student:Light pollution, right? From street lights and stuff ...

Professor:Yes, Especially unshielded street light, you know, ones that aren’t pointed downward. Now, here’s an irony, the buiding we are in now, the astronomy building not far from our observatory, has unshielded lights.

Student:So the problem is pretty widespread.

Professor:It is basically beyond control, as far as expecting to view the night sky anywhere near city, I mean. I have lived around here my whole life. And I have never seen the Milky Way within city limits, and I probably never will. There is a price for progress, eh? But let’s think beyond light pullution, that’s only one kind of a technological advance that has interfered with astronomical research. Can anyone think of another? No? Ok, let’s look at it this way, we don’t only gain information by looking at the stars, for the past 70 years or so, we have also used radio astronomy1 , which lets us study radio waves from the sky.

Student:How can you observe radio waves? I mean, tell anything about the stars from that.
  
Professor:
Well, in optical astronomy, using a telescope and observing the stars that way, we rely on visible light waves. What we are seeing from earth is actually electromagnetic radiation that’s coming from stars. And just one part of it is visible light. But there are problems with that. When photons2 and light waves hit objects in our atmosphere, water droplets, oxygen and nitrogen molecules, dust particles and so on. These objects are illuminated, they are lit up, and those things are also being lit by all our street lights, by the moon, all these ambient light. And on top of that, when that visible radiation bounces off those molecules, it scatters in all directions. And well, light from stars, even nearby in our own galaxy, doesn’t stand a chance against that. Basically the light bouncing off all these objects close to earth is brighter than what’s coming from the stars. Now, radiowaves are electromagnetic radiation that we can’t see. Nearly all astronomical objects in space emit radio waves, whether nearby stars, objects in far away galaxies, they all give off radio waves. And unlike visible light waves, these radio waves can get through the various gases and dusts in space, and through our own earth’s atmosphere comparatively easily.

Student:Ok, then we might as well give up on optical astronomy and go with radio astronomy.

Professor:Well, the thing is, with the radio astronomy, you can’t just set up a telescope in you backyard and observe stars. One problem is that radio waves from these far away objects, even though they can get through, are extremely faint. So we need to use radio telescopes, specially designed to receive these waves and then, well, we can use computers to create pictures based on the information we receive.

Student:That sounds cool. So, how do they do that?

Professor:Well, it is kind of like the same way a satellite dish3.receives its signal, if you are familiar with that. But radio telescopes are sometimes grouped together, is the same effect as having one big telescope to increase radio wave gathering power. And they use electronics, quite sophisticated. Yeah, it is neat how they do it, but for now why don’t we just stick with what we can learn from it. Some very important discoveries have been made by this technology, especially you consider that some objects in space give off radio waves but don’t emit any light. We trouble discovering those sorts of bodies, much less studying them using just optical telescopes.

Student:Well, If the radio waves are so good at getting throught the universe, what’s the problem?

Professor:Well, answer this. How come people have to turn off their cell phones and all our electronic devices when an airplane is about to take off?

Student:The phones interfere with the radio communication at the airport, right?

Student:Oh, so our radio waves here on earth interfere with the waves from space?

Professor:Yes, signal from radios, cell phones, TV stations, remote controls, you name it. All these things cause interference. We don’t think about that as often as we think about light pollution. But all those electrical gauges pollute the skies, just in a differen way.

 

1 What is the lecture mainly about?

A. Recent advances in technology used by astronomers

B. How radio astronomy has led to advances in communication technology

C. Important discoveries made by radio astronomers

D. Difficulties astronomers have in observing the universe

 

2 What is the professor's attitude about light pollution in cities?

A. He feels that it should be carefully regulated.

B. He believes it is unfortunate

C. He thinks astronomers have not dare enough to address the issue

D. He believes that the severity of the problem is often exaggerated. 



3 According to the professor, why are radio waves particularly useful for astronomical observations? Click on 2 answers

A. Some astronomical bodies emit radio waves but not visible light

B. Radio wanes provide more information about star composition than visible light waves do

C. Radio waves can be defected with simple equipment.

D. Radio wanes can pass through panicles in space



4 What does the professor imply is an advantage of optical astronomy over radio astronomy?

A. It allows far more precise observations.

B. It is better for making observations within our own galaxy.

C. It requires less sophisticated equipment.

D. It is not affected by the weather.



5 According to the professor, why do radio astronomers sometimes have difficulty studying very distant objects? Click on 2 answers

A. Signals from closer objects interfere with radio waves from space.

B. Particles in the atmosphere change the direction of radio waves.

C. Radio waves from space are not very strong.

D. Light waves from sources on Earth alter radio waves from distant objects