How do rainbows occur?

Your question of the month in January (2016)
Colin, 8 years old

When it is raining and the sun is shining at the same time - do you sometimes look into the sky and keep your eyes peeled for a rainbow too? But how do these pretty, colourful "bows" actually occur? We will explain it to you.

First of all: sunlight is not white as it might appear at the first glance. It is actually made up of lots of different colours. But our brains perceive these bundled colours as being "white". We can only see the different colours when the light "breaks up".



This happens for example if it meets a raindrop: it enters the raindrop and is then first broken up (deflected). The light is mirrored in the raindrop and reflected by the outside wall of the raindrop. When it then leaves the raindrop again, it is broken down a second time. That always happens when light moves from one material (e.g. water) into another (e.g. air).

If the sunlight hits a raindrop it is broken down by refraction into its individual components (colours). That is why you can only ever see a rainbow if you have the sun behind you and the rain in front of you: the sunlight shines onto the rain in front of you, is mirrored in the raindrop and then the different colours are reflected back to you.


Rainbows always have the same colour pattern: it starts at the top with red, then orange, yellow, green, blue and violet. By the way: the appearance of a rainbow depends on where you are standing. The higher up you are, the further up it stretches into the sky. If you see one from a plane, it even forms a closed circle - maybe you will be lucky on your next flight and can see one!