A colored ring around the Sun with an apparent radius of about 46 degrees is a 46° halo.
This rare halo forms when sunlight passes through randomly oriented, hexagonal ice crystals in high clouds such as cirrus. Light enters through one prism face and exits through the crystal’s hexagonal base. The approximately 90-degree angle between those faces creates a much wider ring than the familiar 22° halo.
The 46° halo is usually fainter and less frequently seen than its 22° counterpart. Its colors can be more widely dispersed, but the outer edge is often diffuse because many rays are deviated through angles greater than the minimum-deviation angle. The phenomenon is a refraction effect, not a colored cloud or a rainbow.
Observers can confuse it with supralateral and infralateral arcs, which may appear in the same region of the sky. Their shape and dependence on solar elevation help distinguish them. French physicist Edmé Mariotte gave the first explanation of the 46° halo’s ice-crystal refraction in 1679.