TOEFL Listening Practice: Lecture17
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Transcript
| Professor: | Good morning, everyone. Today we’ll be discussing the great depths of space. First of all, I’d like you to remember the last time you went outside on a dark night when the sky was clear. Did you look up? Could anyone see the Milky Way Galaxy? Shouldn’t we be able to see it, since we’re inside it? What do you think? |
| Jack: | I’ve heard Light Pollution blamed quite a bit, for being unable to see the stars. Street lamps and stuff. |
| Professor: | Exactly right. Especially from exposed street lamps, the ones that shine in all directions instead of straight down. Want to hear something funny? The astronomy building down the road, where they look up into the sky to take readings, has unshielded street lights right next to it. The problem is widespread, and pretty much beyond our control if you’re looking at the sky near a city. Unless there’s something dramatic like a power outage, it’s likely we’ll never be able to see the stripe of stars that is an arm of our Milky Way from within the city limits. |
| Okay, beyond pollution, what other technological invention that has caused some intervention in space observation? Anyone? Well, let’s look at it this way; we don’t gain information just from looking at the stars through a telescope. For the last 70 years, we’ve also been using radio astronomy. Yes! Jack! You got a question? | |
| Jack: | How would that even work? Radio waves from the stars? Don’t we produce those? |
| Professor: | We do indeed create radio waves with some human inventions, but they’re also a naturally occurring phenomenon. |
| Optical Astronomy, the type you’re thinking of, we use a telescope and lenses to get a close-up look at visible light reaching the earth. That light is actually made of electromagnetic radiation from the stars. However, there are some major flaws with that kind of viewing, if one wants to be as accurate and precise as possible in measurements. When photons and light waves strike particles or objects in our atmosphere, they are illuminated. The list of interfering particles is varied, and includes dust, water droplets, even nitrogen and oxygen molecules. It’s not stars shining on these things, but those open street lamps we mentioned earlier, and the reflected light of the moon. | |
| On top of being lit from below, when visible light strikes those molecules, it scatters. The biggest problem is that starlight is very faint compared to the bright, newly-generated lights coming from our own surface. | |
| Now, a type of electromagnetic radiation that doesn’t require our eyes or traveling light is radio waves. Just about every astronomical object in space will emit some sort of radio wave. Stars, objects in other galaxies, nebulas, they all give off radio waves. Unlike visible light, radio waves can travel right through foreign particles, and cut right through any interfering light that may seem brighter due to proximity. | |
| Woman: | So! Why do we still use telescopes if radio astronomy is so much more effective? |
| Professor: | The problem is, you can’t just set a radio receiver up in your backyard and check out the stars. While plenty of radio waves may be reaching earth, they came from such a long ways off and end up very faint. To observe radio waves, you need a special kind of telescope, a bit like a satellite dish, designed to receive those waves. After that, we use complex computers to generate images from the gathered data. |
| Radio Telescopes are often grouped together, the many smaller dishes doing the work that one bigger, more expensive dish would do. They calibrate them so that they are aligned, and their receivers blend the incoming data just so. The computers parse together the data and are able to create one solid, detailed picture. | |
| Well, what can we learn from this technology? A few important discoveries have been made, especially now that we’ve learned some astronomical bodies give off radio waves, but not light. We had a lot of trouble discovering those entities before, and next to zero luck examining them with optical telescopes. | |
| Now, why do you think radio waves may have interference, even if they’re so good at cutting through solid matter? | |
| Jack: | Radio interference? Like, the same reason we have to turn our cell phones off when a plane takes off. |
| Professor: | Exactly. Cell phones, radios, TV stations, Gameboy linking, anything that isn’t a direct cord, it can generate energy to interfere with radio waves. While radio may pass swimmingly through solid objects, energy gives it a bit of a problem. While it’s easy to see and think about light pollution, technology continues to pollute the sky in a different way. |
| I mean, think about it. At this very moment, within a classroom, there’s wifi available, right? That means, inside your bodies, humming through your veins and muscles is the same internet signals you’re able to tap into with your computers. |