Hexagonal column crystals form the lower and upper tangent arcs. As they slowly drift downwards relative to air currents, aerodynamic drag orients them so that their long axes are almost exactly horizontal.
Rays enter and leave side faces inclined at 60 degrees to each other.
The tangent arcs change shape dramatically with the sun's altitude. They join when the sun reaches 29 degrees to form the circumscribed halo.
The blue circle represents the common 22 degree circular halo. It is absent in Dario's images.
