· How do bright rings around the Sun originate?
“I have seen bright rings appear around the Sun. What do the rings consist of, and why do they appear?”
Bright rings around the Sun are known as halos. The rings originate when sunlight is bent by ice crystals high up in the atmosphere. The ice crystals are often hexagonal, plate- or pencil-shaped and normally exist in connection with high-lying cirrus clouds. These are formed by water vapour, and have thread-like structures. The ice crystals in the clouds function as small prisms that bend the sunlight at specific angles.
It is fairly common to witness a 22° solar halo in the sky, formed when the sunlight is bent 22 degrees. There are often two bright spots at the edge of the ring in connection with a 22° solar halo, and these spots are also known as ‘mock suns’ or ‘sun dogs’.
A slightly rarer sight is a 46° halo, in which the light is bent 46 degrees, so that the bright ring is further away from the Sun. Even rarer is a 9° halo in a ring closely around the Sun. Such 9° halos originate only when the sunlight is refracted in pyramid-shaped ice crystals.
Halos most often originate in the winter, when temperatures are low and the Sun is low in the sky. The bright rings are not only observed around the Sun, but also the Moon, where the same hexagonal ice crystals in thin cirrus clouds can cause the phenomenon.
1 22° HALO:
The most ordinary and clear halo is located 22 degrees from the Sun. That is the angle at which light is typically bent as it passes through hexagonal ice crystals.
2 RED AND BLUE:
Sunlight includes all colours. Blue light is bent slightly more than red light, and so a halo will appear reddish closest in and bluish farthest out.
3 MOCK SUNS:
Mock suns or sundogs originate on either side of the Sun when the sunlight passes through flat hexagonal ice crystals that descend down through a cloud.
4 46° HALO:
A rare weak outer ring known as a 46° halo forms when sunlight takes a route through the ice crystals which results in a light bend of 46 degrees.