You found out how the auroras are formed. Now you will learn about rainbows.
Rainbows are not formed in the practical meaning of existence, i.e. they are not real. They belong to what we usually call optical illusions. Rainbows are caused by the reflection and refraction of light in water droplets. After this the light scatters into different colors because different colours have different wavelengths. This means that they will leave the water droplet at different angles hence making a “colour palette” (ROY G. BIV). 
What is even more interesting is that the rainbows are full circles… Want to know more? Watch this two videos of SciShow!
As always I hope you learnt something new! 🙂 
Minutephysics has just made a wonderful video explaining the origins of the acronym ROY G. BIV. Watch it!
I’m going to categorize this under the week themes despite the fact that it doesn’t fulfill the requirements for it (i.e. it wasn’t posted during that time).
References and further reading.
 – Rainbow – Wiki
 – See the references in the descriptions of the videos (open the videos on youtube)