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Speaker 1: Get smarter in sixty seconds with brain Stuff from how

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Speaker 1: stuffworks dot com. I am Marshall Brain Today's question, why

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Speaker 1: is the sky blue? Here's something interesting to think about.

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Speaker 1: When you look at the sky at night, it is black,

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Speaker 1: with the stars in the moon forming points of light

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Speaker 1: on that black background. So why is it that during

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Speaker 1: the day the sky does not remain black with the

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Speaker 1: Sun acting as another big point of light. That's exactly

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Speaker 1: what happens on the moon. So why on Earth does

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Speaker 1: the daytime sky turn a bright blue and all the

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Speaker 1: stars except the Sun disappear during the day. The first

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Speaker 1: thing to recognize is that the Sun is an extremely

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Speaker 1: bright source of light, much brighter than the other stars.

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Speaker 1: The second thing to recognize is that the atoms of

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Speaker 1: nitrogen and oxygen in the atmosphere have an effect on

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Speaker 1: the sunlight that passes through them. There is a physical

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Speaker 1: phenomenon called ray Leigh scattering that causes light to scatter

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Speaker 1: when it passes through particles that have a diameter one

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Speaker 1: tenth that of the wavelength or color of the light.

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Speaker 1: Sunlight is made up of all different colors of light,

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Speaker 1: but because of the elements in the atmosphere, the color

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Speaker 1: blue is scattered much more efficiently than the other colors.

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Speaker 1: So when you look at the sky on a clear day,

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Speaker 1: you can see the sun is a bright disk. The

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Speaker 1: blueness that you see everywhere else is all of the

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Speaker 1: atoms in the atmosphere scattering blue light towards you. Because

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Speaker 1: red light, yellow light, green light, and the other colors

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Speaker 1: aren't scattered nearly as well, we see the sky is blue,

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Speaker 1: and that blue color is so bright that it completely

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Speaker 1: blots out all the other stars because they're so dim.

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Speaker 1: Do you have any ideas or suggestions for this podcast?

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Speaker 1: If so, please send me an email at podcast at

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Speaker 1: how stuff works dot com. For more on this and

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Speaker 1: thousands of their topics, go to how staff works dot com.

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Speaker 1: MHM