• Question: What is the significance of red sky at nightfall?

    Asked by harzard456 to Mike, Pip, Tianfu, Tim, Tom on 3 Jul 2012.
    • Photo: Tim Stephens

      Tim Stephens answered on 3 Jul 2012:

      It’s to do with the way that light is scattered by the atmosphere – the process’ name is Rayleigh scattering. When white sunlight hits the atmosphere, the blue colours are scattered more sideways than the reds.
      At sunset, you can look towards the sun and see that the remaining red light is around the sun, but the blues have been scattered earlier in the atmosphere and are making the sky blue for people further round the earth.

      In Britain, the weather comes mostly from the Atlantic (west) side, which is also where the sun sets. If you get a nice red sunset, it means that there aren’t many clouds in that direction and that the weather is going to be nice for a few more hours at least.

      I don’t think that there have been many nice sunsets this summer 🙁

    • Photo: Tom Lister

      Tom Lister answered on 3 Jul 2012:

      Shephards delight! The scatter that is mainly responsible for a red sunset is caused by moisture and dust in the air (Mie scattering, which is similar to Rayleigh but for slightly bigger particles).

      Why does this mean a nice day the next day? I don’t know but Tim’s answer looks ok.

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