[MUSIC PLAYING]
Hey, everybody.
I'm Ben, and here's
today's question.
Why is the sky blue?
This is one of those
questions that four-year-olds
ask all the time,
and it's something
interesting to think about.
So let's start here.
When you look at the
sky at night it's black,
and there are stars,
and there's the moon,
and they form these points of
light on that black background.
So why is it that during the
day the sky doesn't remain black
with the sun acting like
just another point of light?
I mean, that's exactly
what happens on the moon.
So why on Earth--
huh, on Earth--
does the daytime sky turn a
bright blue, and all the stars
except for the sun seem to
disappear during the day?
There's a couple things
we have to recognize.
First, the sun is an extremely
bright point of light.
It's also much closer to Earth.
The second thing to recognize
is that the atoms and nitrogen
and oxygen in the
atmosphere have
an effect on the sunlight
that passes through them.
Also, there's
scattering that causes
light to scatter throughout
the sky when it passes
through particles that
have a diameter that's 1/10
that of the wavelength or
the color of the light.
Now, sunlight is made up of
all different colors of light.
But because of the
elements in our atmosphere,
the color blue is scattered
much more efficiently
than all of the other colors.
So when you and I look at
the sky on a clear day,
we can see the sun
as a bright disk.
And that blueness that
we see everywhere else
is all of the atoms in
the atmosphere scattering
blue light toward us.
And that's because red light,
yellow light, green light,
all of the other colors are
not scattered nearly as well
and we see the sky
as blue as a result.
And that blue color is so
bright that it completely
blots out all the other
stars because they're
so dim in comparison.
So that's it.
That is why the sky is blue.
Thanks so much for watching.
We hope you enjoyed
this episode.
And as always, you know
what I'll say at this point.
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These videos are cool.
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You know, I feel safe saying
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are cool.
