• Question: why is the sky blue?

    Asked by cyoung to Alice, Bose, Christian, Emma, Steve on 5 Mar 2016.
    • Photo: Steve Marsden

      Steve Marsden answered on 5 Mar 2016:

      Light that passes through the atmosphere doesn’t always travel in a straight line to the surface. A lot of the time it will be scattered as it passes through the air. Blue light scatters far more readily than the other colours, giving the entire sky a blue tint.

      If you were to look at the sun from space, it would appear a brilliant white, but from the surface of Earth, it takes on more of a yellow/red tint. This is because the blue light from it is being filtered out and spread over the entire sky.

      This doesn’t just happen with the sun though. When the moon is low on the horizon the moonlight has to pass through more of the atmosphere, and so more of the blue light is scattered. This leaves the moon with a vivid red colour.

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