• Question: why is the sky blue?

    Asked by xheneta1 to Dilwar, Lou, Rachel, Simon, Susan on 16 Nov 2013. This question was also asked by delaram123.
    • Photo: Susan Skelton

      Susan Skelton answered on 16 Nov 2013:

      Hi xheneta and delaram!

      When we look up at the sky, we see the light that came from the sun, all the way through space, through the atmosphere, and down into our eyes.

      The light from the sun looks white but it is actually made up of all the colours of the rainbow added together. (We can separate these colours to see them if we put a glass of water on a white piece of paper in bright sunlight.)

      When the light from the sun passes through the atmosphere it bounces around as it gets scattered by all the molecules in the air. Blue light is bounced around much more than any other colour of light, so the blue light is scattered in all directions. This is why, when the sun is high in the sky, we see the sky as blue!

      But something different happens when the sun is close to the horizon at sunset and sunrise. Sunlight from the low Sun has to pass through much more atmosphere before it reaches you. By the time it reaches your eyes, most of the blue light has already been scattered which leaves only the red light. This causes the beautiful colours we see in the sky at sunset and sunrise.

    • Photo: Simon Langley-Evans

      Simon Langley-Evans answered on 16 Nov 2013:

      I wonder what colour the sky would be on other planets and moons in our solar system. The blue that we see is because of the bounce of the light off the molecules that make up the atmosphere. On the Moon where there is no atmosphere the sky is black. But what about Mars? I think that a lot of the pictures that I have seen show it as yellow/orange which I think is caused by the dust in the atmosphere, which contains a lot of iron oxide.

      Titan, which is a moon of Saturn, which has a very thick and dense atmosphere, has a sky which is a bit like ours at sunset. Susan explained that the sky and sunset is orange/red because the light comes through a thicker atmosphere- well on Titan it would be like that all day. Venus also has a red sky, and if you stood on the surface you would never see the sun because there is too much cloud.

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