What colour is the sky behind the rainbow?

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Offline thedoc

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What colour is the sky behind the rainbow?
« on: 12/05/2016 17:50:01 »
Rohan asked the Naked Scientists:
   What color is the sky behind the rainbow?
What do you think?
« Last Edit: 12/05/2016 17:50:01 by _system »

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Offline evan_au

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Re: What colour is the sky behind the rainbow?
« Reply #1 on: 12/05/2016 22:12:18 »
I think the background would be blue (for clear sky) or grey (for grim dark clouds) or green (if you produce the rainbow at home while watering the garden).

The rainbow is produced by sunlight striking raindrops and being reflected and refracted within the raindrop, back towards your eye.

However, the density of raindrops is very low, so considerable light from beyond the raindrops continue towards your eye. So you see the rainbow overlaid on whatever the background color, whether that be blue or grey (or green).

But the most spectacular rainbows occur when the background is thick clouds which are themselves in shadow, producing a very high contrast. This is the best opportunity to see double rainbows.

See: https://en.wikipedia.org/wiki/Rainbow#Variations