Rainbows

For most people, the most easily recognisable atmospheric optical phenomenon is the rainbow. Rainbows are seen when the sun is behind you, and there are raindrops in front of you. The droplets reflect the light back towards you.

What causes the bright colours of a rainbow?

Light coming from the sun contains all of the colours in the spectrum. When the light from the sun enters a raindrop, it is ‘refracted’ (or bent). Different colours of light are refracted by slightly different amounts.

The light then reflects off of the back of the raindrop, and is refracted once more when it exits the raindrop and heads back towards your eyes. Because the light has been refracted (twice), the different colours of light reach our eyes at slightly different angles, creating the spectrum we see as a rainbow. This process is depicted in the diagram below:

The photo below shows a double rainbow. The outer rainbow is created by light being reflected twice within the raindrop.

Photo by Jacquie Flynn in Taranaki in October 2016.