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Pollution and Sunlight

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Subido el 28 de mayo de 2007 por EducaMadrid

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NASA Why? Files segment explaining how sunlight and aerosols create the colors of the sky.

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Hi, kids. I'm Peter Poluski at NASA Ames Research Center. 00:00:00
I study light in the Earth's atmosphere. 00:00:05
What can I do for you today? 00:00:07
We're trying to figure out a problem, 00:00:08
and we need to know why the skies are blue during the day. 00:00:10
Good question. 00:00:13
Let me first talk to you about the sun. 00:00:15
It's a white light, which means it's really a mixture 00:00:17
of all colors of the spectrum, from blue to red. 00:00:20
If the sunlight is white, then why is the sky blue? 00:00:23
We learned about reflection at the Jefferson Lab. 00:00:26
Could the sky be blue because it's reflecting blue off the ocean? 00:00:28
No, that's a common misconception. 00:00:32
The Earth has an atmosphere, 00:00:34
which is made up of molecules such as oxygen and nitrogen. 00:00:36
It's also made up of tiny little microscopic particles, 00:00:39
and these tiny little microscopic particles in the atmosphere 00:00:42
are called aerosols. 00:00:45
I don't see anything in the air. 00:00:46
Well, let me ask you first, what do you know about light? 00:00:48
We learned at the Boston Museum of Science 00:00:51
that light is a wave and that it is made up of photons. 00:00:53
Occasionally, the photons will actually bounce off of the molecules 00:00:56
and particles and go off into different directions. 00:00:59
That's something that we call scattering. 00:01:02
Let me show you an experiment I have set up here. 00:01:04
This fancy instrument is something we call a sun simulator, 00:01:08
but really it's just a lamp which sort of mimics the output of the sun. 00:01:11
First of all, you can see the beaker here 00:01:16
has very little light scattering out of the sides of it. 00:01:19
Now watch what happens when I add some milk to the beaker. 00:01:22
What does the milk represent? 00:01:25
The molecules and particles in the atmosphere. 00:01:27
Now we've got plenty of light scattered out the sides, 00:01:30
and notice it's very bluish. 00:01:32
When we look at the sunbeam that's been transmitted through the beaker, however, 00:01:34
that's become red. 00:01:38
That's because the blue light's been removed from the beam 00:01:39
and scattered out the sides. 00:01:41
Just like the sky looks blue, but I don't understand. 00:01:43
Remember we said that sunlight is a mixture of all colors. 00:01:46
Now the blue photons will actually scatter off of the particles 00:01:49
much more frequently than the red ones. 00:01:52
That means that we get blue light scattered out 00:01:54
and the red light gets transmitted through. 00:01:57
So why do we see red skies at night and in the morning? 00:01:59
Well, when the sun's near the horizon, 00:02:03
the sunbeam is traveling through a very, very thick portion of the atmosphere. 00:02:05
That's also where most of the particles are concentrated 00:02:08
because gravity keeps the particles near the ground. 00:02:11
That makes sense. 00:02:14
Any event that puts more particles near the horizon 00:02:15
can make the sunset and sunrise even more red than it is usually. 00:02:18
Now, one of those events is a pollution event. 00:02:21
I'm not an expert in pollution, but I happen to know one. 00:02:24
His name is Mark, and he works at the Langley Research Center. 00:02:27
So why don't we give him a call? 00:02:30
This is so cool. 00:02:32
Wow, looks like we found the right place. 00:02:34
Hello, Mr. Vaughn. 00:02:37
Hey, guys. 00:02:38
Well, we need to know more about what causes air pollution. 00:02:39
Mostly when we think about air pollution, 00:02:42
we think about the things that human beings put into the air. 00:02:44
We think about the emissions from factory smokestacks. 00:02:47
They're thinking about the exhaust from automobiles. 00:02:50
But when we actually get down to measuring the aerosol content in the air, 00:02:53
we find out that human beings account for only about 10% of it. 00:02:57
The other 90% comes from Mother Nature herself. 00:03:01
Mother Nature? 00:03:04
But I always thought that nature was clean and natural. 00:03:06
Think about a volcano going off. 00:03:08
It's not just lava that comes out of it. 00:03:10
It also spits blistering hot gases way, way, way up. 00:03:12
And those gases react with water vapor 00:03:16
to form little tiny sulfuric acid droplets 00:03:18
that can hang around in the stratosphere for years. 00:03:21
Or think about big dust storms coming across the desert. 00:03:24
How do you know how much dirt is in the air? 00:03:27
Matthew, you'd be a cloud with a squirt bottle. 00:03:30
PJ, you are going to be a lidar with a laser. 00:03:34
And I'm going to stand here with my flower and be a dust storm. 00:03:37
Wow, they look like sparkles. 00:03:43
I bet they do. 00:03:45
We use a very similar technique 00:03:46
when we measure real aerosols in the atmosphere. 00:03:48
Only then we use machines called a lidar. 00:03:51
Come on, I've got one right over here I can show you. 00:03:54
Wow, that's a big machine. 00:04:00
What does it do? 00:04:02
What we do is fire pulses of laser light 00:04:03
out of the laser and right to this turning mirror here. 00:04:06
From there, they shoot straight up into the atmosphere. 00:04:08
Just like we saw the sparkles off of aerosols in our little experiment, 00:04:12
we use our telescope to look at the sparkles 00:04:16
off of real aerosols in the atmosphere. 00:04:19
Could the aerosols from pollution 00:04:22
cause the sky to turn red during sunrises and sunsets? 00:04:24
Sure, sure they can. Circumstances are right. 00:04:27
We learned from Dr. Poluski 00:04:30
that aerosols scatter more blue photons 00:04:32
and leave the red ones for us to see. 00:04:34
Oh, absolutely. 00:04:36
If you increase the number of small particles up there, 00:04:37
they will scatter away more blue light 00:04:40
and you will see more red. 00:04:42
Thank you. We learned a lot. 00:04:44
Good. Good luck on your project. 00:04:46
Bye. 00:04:48
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Idioma/s:
en
Niveles educativos:
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Autor/es:
NASA LaRC Office of Education
Subido por:
EducaMadrid
Licencia:
Reconocimiento - No comercial - Sin obra derivada
Visualizaciones:
342
Fecha:
28 de mayo de 2007 - 15:32
Visibilidad:
Público
Enlace Relacionado:
NASAs center for distance learning
Duración:
04′ 49″
Relación de aspecto:
4:3 Hasta 2009 fue el estándar utilizado en la televisión PAL; muchas pantallas de ordenador y televisores usan este estándar, erróneamente llamado cuadrado, cuando en la realidad es rectangular o wide.
Resolución:
480x360 píxeles
Tamaño:
28.97 MBytes

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