Speaker 1: Get smarter in sixty seconds with brain Stuff from how
Speaker 1: stuffworks dot com. I am Marshall Brain Today's question, why
Speaker 1: is the sky blue? Here's something interesting to think about.
Speaker 1: When you look at the sky at night, it is black,
Speaker 1: with the stars in the moon forming points of light
Speaker 1: on that black background. So why is it that during
Speaker 1: the day the sky does not remain black with the
Speaker 1: Sun acting as another big point of light. That's exactly
Speaker 1: what happens on the moon. So why on Earth does
Speaker 1: the daytime sky turn a bright blue and all the
Speaker 1: stars except the Sun disappear during the day. The first
Speaker 1: thing to recognize is that the Sun is an extremely
Speaker 1: bright source of light, much brighter than the other stars.
Speaker 1: The second thing to recognize is that the atoms of
Speaker 1: nitrogen and oxygen in the atmosphere have an effect on
Speaker 1: the sunlight that passes through them. There is a physical
Speaker 1: phenomenon called ray Leigh scattering that causes light to scatter
Speaker 1: when it passes through particles that have a diameter one
Speaker 1: tenth that of the wavelength or color of the light.
Speaker 1: Sunlight is made up of all different colors of light,
Speaker 1: but because of the elements in the atmosphere, the color
Speaker 1: blue is scattered much more efficiently than the other colors.
Speaker 1: So when you look at the sky on a clear day,
Speaker 1: you can see the sun is a bright disk. The
Speaker 1: blueness that you see everywhere else is all of the
Speaker 1: atoms in the atmosphere scattering blue light towards you. Because
Speaker 1: red light, yellow light, green light, and the other colors
Speaker 1: aren't scattered nearly as well, we see the sky is blue,
Speaker 1: and that blue color is so bright that it completely
Speaker 1: blots out all the other stars because they're so dim.
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Speaker 1: MHM