sentences:  A 22° halo may be visible on as many as 100 days per year – much more frequently than rainbows.Even though it is one of the most common types of halo, the exact shape and orientation of the ice crystals responsible for the 22° halo are the topic of debate.Hexagonal, randomly oriented columns are usually put forward as the most likely candidate, but this explanation presents problems, such as the fact that the aerodynamic properties of such crystals leads them to be oriented horizontally rather than randomly.