Question: how is it that you can have more than one rainbow at the same time?

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  1. Know what a prism does? It’s a block of glass that splits light into its separate bits, so you can see the different colours. red, orange, yellow etc. The light we see is a mix of all those colours so we don’t see them alone, but if you pass light through something with a certain structure, then you can see them split.

    Raindrops do this very nicely. Sunlight comes along and hits a raindrop. The light splits into its separate bits (by refraction). The different bits of the light bounce off the back of the raindrop (staying inside) and come back out the front. This doesn’t always happen, but if the direction of light is right, and the size of the drop is right, you can get the light bouncing around like this. That’s why when you see a rainbow, the sun is always behind you. The light bounced off the back of the raindrop back into your eye.

    Sometimes that happens as well as something else. Sometimes the light bounces off the raindrop inner surface twice. So light goes in, splits, bounce, bounce, and out. The angles aren’t quite the same, which is why the second rainbow appears at a different place. Each time the light bounces, the order of the colours changes – you can play with a prism and a mirror yourself to check this out. So the colour order in the second rainbow is the other way around.

    These things happen at lots of different angles, which is why it doesn’t matter if you move, or you’re driving. There will always be some angle where the rainbow works if the sunlight’s at the right angle. Also, the fact that the whole thing is caused by a curved raindrop is part of the reason the rainbow itself is bow-shaped. So the curve of the drop is causing the curve of the ‘bow.


  2. Great answer Matt. Here is more information


  3. There were two leprechauns out that day with their pots of gold 🙂

    Nah just kidding (obviously! Leprechauns are trading in platinum these days, it’s worth more) but I think Mat has explained it pretty well already.