What are double rainbows?
On a tour of the Cabot Trail, Guy and Marie Atkins of Saint John, New Brunswick saw two striking rainbows almost side by side. They wanted to know how unusual was their sighting. Double rainbows are not unusual, in fact, they occur with every rainbow. It’s just that they are rarely bright enough to be seen. Dale Little of Sidney BC also wanted to know how double rainbows form. When white sunlight enters each raindrop, it bends. The bending breaks light into its rainbow colours. The light then reflects off the back of the raindrop. On leaving the drops the light bends again. [Each raindrop scatters the full spectrum of colours, but you will see only a single colour from each drop]. Sometimes light reflects twice inside the raindrop. This action will form two rainbows: a primary rainbow that is produced by the first reflection of light and a larger secondary bow above the first, produced by the second reflection. Colours in the secondary bow are in reverse order to those in the primary r
Double rainbows are not unusual; in fact, they occur with every rainbow but are rarely bright enough to be seen. When white sunlight enters each raindrop, it bends, breaking light into its rainbow colours. The light then reflects off the back of the raindrop and, on leaving the drop, the light bends again. Each raindrop scatters the full spectrum of colours, but only a single colour from each drop is seen. Sometimes light reflects twice inside the raindrop. This action forms two rainbows: a primary rainbow that is produced by the first reflection of light and a larger secondary bow above the first, produced by the second reflection. Colours in the secondary bow are in reverse order to those in the primary rainbow, with red on the inside and violet on the outside. Since only a small number of rays experience this double reflection, the secondary bow is always fainter than the primary.
