How a rainbow forms

In short: A rainbow forms when sunlight is refracted in raindrops, reflected inside and refracted again on leaving. The light is split into its colours in the process.

In more detail: You only see the arc with the Sun behind you and rain in front. The viewing angle from the direction of the Sun is about 42 degrees.

In detail

• Order of colours: Red on the outside, violet inside. Each colour is refracted by a different amount (licht-und-farben).
• Secondary rainbow: With double reflection a second, weaker arc with reversed colour order appears.
• Full circle: From the air, for example from a plane, you can see the rainbow as a complete circle.
• No end: Each observer sees their own bow. You cannot reach it.
• Similar effects: Halos around the Sun and fogbows arise from ice crystals or very small droplets.