Why is the sky blue?
(Lansing State Journal, May 03, 1995)
The sky above us is filled with air. When sunlight shines on the Earth, some of it interacts with the molecules of air. When most of the visible light seems to shine right on through, much of it is actually scattered by the air molecules. The scattered light is mostly blue, so the sky above us looks blue.
At night, there really is not enough light to notice the scattering with the naked eye, so the sky looks black.
When astronauts fly into space the sky above them looks black, like a starry moonless night. This is because out in space there is no air, so the light isn't scattered.
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