How do double rainbows form?

A beautiful “double rainbow” has been snapped on the horizon in Rheine, Germany. Do you know how they appear?

Let’s start with a standard rainbow. To see a rainbow, the sun must be behind the observer. The raindrops refract the sunlight, break it down into its basic colours and reflect them.

The rainbow appears to us from the outside inwards in the following colours: red, orange, yellow, green, blue and finally violet. The lower the sun is, the bigger the rainbow appears.

So how do double rainbows form?

Sometimes you can see another so-called secondary rainbow next to the main rainbow. This is located above the main rainbow at an angle of 51 degrees.

The second rainbow is created by another reflection within the raindrop. The path of the light is thus longer and part of the light is lost. Therefore, the second rainbow appears only fainter, if at all.

At the same time, the colours in the secondary rainbow are arranged in reverse to those in the main rainbow.