White rainbow

A white rainbow or a rainbow of fog is a rainbow-like phenomenon, however, as its name suggests, it appears as a rainbow in fog rather than rain. Due to the very small size of the water droplets that cause a fog (less than 0.05 mm) the fog rainbow has very faint colors, and sometimes it is just white.

The white rainbow is often visible from an airplane flying over sunlit clouds. Sometimes, especially during sunrise or sunset, the white rainbow can be visible to a ground observer, sometimes with a reddish color. It can appear in Altocumulus, Altostratus or Stratus clouds, where the sun shines below and at the edges.

The white rainbow is seen in the same direction as the ordinary rainbow, so the sun would be behind the viewer's head. The size of the white rainbow is slightly smaller than that of an ordinary rainbow.