![cover image](https://wikiwandv2-19431.kxcdn.com/_next/image?url=https://upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Tangent_arc_over_San_Francisco_Bay.jpg/640px-Tangent_arc_over_San_Francisco_Bay.jpg&w=640&q=50)
Tangent arc
Atmospheric optical phemonenon / From Wikipedia, the free encyclopedia
Tangent arcs are a type of halo, an atmospheric optical phenomenon, which appears above and below the observed Sun or Moon, tangent to the 22° halo. To produce these arcs, rod-shaped hexagonal ice crystals need to have their long axis aligned horizontally.[2]
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/9/9e/Tangent_arc_over_San_Francisco_Bay.jpg/640px-Tangent_arc_over_San_Francisco_Bay.jpg)
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/f/fc/Upper_tangent1.jpg/640px-Upper_tangent1.jpg)
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/b/b4/HaloSantaRosa.png/640px-HaloSantaRosa.png)
![Thumb image](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f7/Sun_halo_optical_phenomenon_edit.jpg/640px-Sun_halo_optical_phenomenon_edit.jpg)
Photo: Cindy McFee, NOAA, December 1980.[1]