Rainbow is a natural phenomenon, always pleasing to eyes with bright colors? It turns out that this is not always the case. Sometimes there may be a phenomenon that is called the "white rainbow" or "foggy rainbow".
White rainbow in its form is an absolute copy of the ordinary color rainbow. The process of their formation is similar, which involves sunlight and water drops. That's just the size of the drops in the white rainbow is much less - only 20-25 microns.
In the usual rainbow, white sunlight passing through water drops is refracted and disintegrated by the components of its colors. In other words, there is a dispersion of light. But if the size of the drops is too small, then this phenomenon is entering as Light diffraction.
A bundle of light passing through a sufficiently small water drop is expanding as it is further distributed, intersecting and mixing with other beams of light. Mixing colors in the end and gives that white color to which the white rainbow differs from the usual.
Interestingly, the smaller the size of water droplets, the whiter will seem the observed rainbow. Usually, drops of such small size can be in the fog, so this type of rainbow most often appears when weak, barely lit-out mistlight illuminated by sunlight.