The Prism

Something similar happens with the raindrops. Similar to the prism, light is refracted while passing through the boundary between the air and the water. Because different components of light are refracted differently again, the light is split into its spectral colours. Afterwards the light is reflected at the back of the raindrop.

Light leaves a prism on the opposite side of the light source. In a raindrop, light leaves on the side it came in through due to the reflection.

Where do you have to stand in relation to the sun and the rain to see the colours of the light?

a) To see a rainbow, the sun has to be behind you while you look at the rainfall.

b) A rainbow becomes visible when you look at the sun through the rainfall.