• Question: If clouds are made of tiny water droplets, then why aren't rainbows always there?

    Asked by megansaurus to Davie, Gemma, James P, James V, Nuala on 27 Jun 2012.
    • Photo: James Pope

      James Pope answered on 27 Jun 2012:

      Hi megansaurus,

      Clouds are made up of tiny water droplets, but they don’t form rainbows, because they are so think barely any sunlight can get through. A rainbow is formed when a beam of sunlight passes through a raindrop and the way the light bends as it travels through the raindrop (a process called diffraction) causes different colour light to escape in different directions.

      When the raindrops are in clouds, then the amount of light getting through is much reduced. Big dark clouds which hold lots of rain, look black or dark grey, because no light is getting through at all, and lighter clouds are white as only white light can get through. The process of diffraction will be occurring, but the other colours of light get absorbed or reflected away.

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