A white arc, with a radius of approximately 42°, centred on the antisolar point. The inner edge is often bluish and the outer reddish. The mechanism is that of the rainbow, but the water-droplet diameter is so small (below about 50 μm) that diffraction broadens the bands of colour until they overlap and appear white. When seen from within cloud or fog, the bow may be a partial or full circle, but when seen from outside (as from an aircraft flying above cloud), it may appear as a hyperbola or ellipse, depending on solar elevation. Also known as a cloud bow.
Subjects: Meteorology and Climatology.