TPO19 lecture 2 16. - 英檢

TPO19 lecture 2 16.

16. according to the prof., why do radio astronomers sometime
have difficulty studying very distant objects

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但這個選項
Radio waves from space are rest very strong

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TPO 19 Lecture 2 Astronomy(Radio Astronomy & Optical Astronomy)

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

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
have 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.


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