In the mid latitudes (temperate zones) circumzenithal arcs are roughly as common as rainbows. It’s also one of the brightest and most colorful of the atmospheric halos and arcs. Yet very few people have ever seen one. read more
For a circumzenithal arc to form, the ice crystals must be at a specific orientation relative to the sun. Light must enter the ice crystal through its flat top face and exits through a side prism face. read more
In fact, the correct term for this meteorological phenomenon is a circumzenithal - or Bravais - arc. Unlike rainbows, where sunlight refracts through raindrops, circumzenithal arcs occur when sunlight refracts through ice crystals, held in cirrus clouds, in a specific way. read more