 Contrary to public awareness, the CZA is not a rare phenomenon, but it tends to be overlooked since it occurs so far overhead.It is worthwhile to look out for it when sun dogs are visible, since the same type of ice crystals that cause them (plate-shaped hexagonal prisms in horizontal orientation) are responsible for the CZA.The light that forms the CZA enters an ice crystal through its flat top face, and exits through a side prism face.