 Circumzenithal arc

The circumzenithal arc, also called the circumzenith arc (CZA), upside-down rainbow, and the Bravais arc, is an optical phenomenon similar in appearance to a rainbow, but belonging to the family of halos arising from refraction of sunlight through ice crystals, generally in cirrus or cirrostratus clouds, rather than from raindrops.The arc is located at a considerable distance (approximately 46°) above the observed Sun and at most forms a quarter of a circle centered on the zenith.