The glory of a circular rainbow
A rainbow gets its traditional semicircle shape from the horizon, which makes it seem as if it is half a circle. So when the same atmospheric conditions that create a rainbow are observed from an airplane, a rainbow can appear to be a full circle. This is called a glory, which NASA defines as an optical phenomenon that "looks like small, circular rainbows of interlocking colors." This glory was photographed from a plane over South Africa.