Why do millions of raindrops only make one rainbow?

10th February 2011
Why do millions of raindrops only make one rainbow? (iStock)

Asked by: Del Nolan, Peterborough

The true figure for the number of raindrops involved is in the trillions, but more importantly, in reality, there’s never just one rainbow. The almost poetic truth is that everyone gets their own unique rainbow.

The reason each of us only sees one is because of the way rainbows are formed. When a ray of sunlight enters raindrops, the different wavelengths of light it contains are bent off-course by different amounts: those corresponding to the colour red being deviated the least, and violet the most. What emerges from the raindrop is thus a spread of colours, each bent through an angle of between around 40° and 42°.

While this happens with every raindrop lit by the Sun, each of us only sees the rainbow formed by those raindrops that happen to be at the correct angular direction to send the different colours into our eyes. So each of us receives our own special rainbow created by a dedicated set of raindrops in the sky. Aaah.


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