A bite-size answer to the question why do we get rainbows…
Image by C. G. P. Grey via Flickr
It’s been raining here again in the UK. But there has been a little sunshine too. On the way home from the zoo last weekend my son spied a beautiful rainbow in the sky up ahead of us and asked “Dad, why do we get rainbows?”
So what’s the answer? Well, to begin, we need to know that white light (e.g. sunlight) is actually made up of a spectrum of colours. Light travels from the Sun to the Earth in waves of different colours. Some light travels in shorter or choppier waves whilst others travel in longer or smoother waves. Different coloured light has different wavelengths – red has long waves, blue has short waves. This phenomenon was explained by Sir Isaac Newton by letting sunlight pass through a prism. When the light passes through the prism, it is refracted (bent) and scattered (known as dispersion). And because different coloured light has different wavelengths and frequencies, the amount by which light is bent varies. This means we can see the ‘split’ or spectrum of colours from which white light is made.
The above principle can help explain how rainbows are formed. When there are water droplets in the air – e.g. during or following rain – light from the Sun penetrates the surface of the drop, a bit like our prism. As it enters, the light is refracted and dispersed before hitting the back of the drop. Most of the scattered light then reflects or bounces off the back of the raindrop, passes back through the front and is refracted again. What we then see in the sky is our rainbow.
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