Question: What causes rainbows?

Shane Mc Guinness answered on 11 Nov 2013:

Amazing question: Basically light from the sun is “white” light. It’s a mix of all the colours we can see (and a lot of those that we can’t!). Each “wavelength” of light has slightly different properties. So when something is able to split all these different types of light we can see them individually. Raindrops do this really well by “refracting” the mix of light and stretching it out into its seperate parts. How does it do this!? Think about a car driving along the road beside the beach. Then the two wheels on the left side start driving on the sand. Because the sand is denser, the wheels travel slower on that side so the car turns! That’s exactly what happens with the light. Because the water of rain drops in the air is higher than air itself, the light bends and splits, like the pages of a book when you bend the book.