SmiLe iN the sky

circumzenithal arcs are a colourful meteorological event. Also known as Bravais’ arcs, the effect occurs when sunlight refracts through ice crystals in a cloud in a certain way. For one to appear, the sun must be more than five and less than 32 degrees above the horizon. This allows its light to enter a horizontal ice crystal through its flat top face. As it passes through and exits through a side prism face, the light is bent and split into the colours of the rainbow. Mainly associated with cirrus clouds, in which ice crystals readily form, the arcs require relatively still conditions. While reasonably common, they are often obscured from view by clouds.