Question: Why is there a rainbow?

Adam Hargreaves answered on 20 Jun 2017:

Rainbows form when sunlight is reflected and refracted through rain droplets. Sunlight is made up of different colours which we normally don’t see, and normally we would call it “white light”. But if that passes through rain droplets at a certain angle, the water splits the light into different colours (a mirror prism does the same thing if you’ve seen one of those). Each colour of light (for example red light, blue light etc.) slow down at different speeds once they pass through the rain drop, which means we see the bands of different colour which make up the rainbow.