The angle of minimum deviation is slightly different for the different coloured components of white light, so the colours are split. Some of the light entering a drop is reflected twice within the drop. As with light undergoing a single reflection, light undergoing two reflections has an angle of minimum deviation. This light forms the secondary rainbow at an angle of about 51 o . The extra reflection reverses the colours from those in the primary bow.
Supernumerary bows are usually faint and are just inside of the primary bow.
They are normally seen as alternating bands of pinks and greens and are caused by interference of light emerging at angles close to the angle of minimum deviation. At such angles different light rays emerge at the same angle but have taken paths of different length through the drop. This leads to a series of bright bands, with the different coloured components having bands in slightly different positions. The brightest rainbows are produced by raindrops of about 1 - 2mm diameter. Larger drops become distorted as they fall and smaller drops cause the colours increasingly to merge, giving rise to a white bow when the drops are about 20 microns in diameter.