The halo around the Sun is produced by the refraction of light in ice crystals, typically found in Cirrus clouds. Cirrus clouds are high-altitude clouds composed mostly of ice crystals rather than water droplets. These thin and wispy clouds are commonly associated with the formation of halos around the Sun.

When sunlight passes through the ice crystals present in Cirrus clouds, the light gets refracted or bent as it enters and exits the crystals. This refraction causes the light to spread out and separate into different colors, similar to how light is dispersed in a prism. This phenomenon results in the formation of a circular halo around the Sun.

The specific shape and characteristics of the halo can vary, but it is typically a ring of light surrounding the Sun, often with a diameter of around 22 degrees. Sometimes, additional arcs or spots of light can be observed within the halo, depending on the orientation and properties of the ice crystals in the clouds.

It`s important to note that the refraction of light by ice crystals in Cirrus clouds is the primary cause of halos around the Sun. While water vapor and dust particles in other types of clouds can also contribute to atmospheric optical phenomena, they are not typically responsible for producing the distinct halo effect seen around the Sun.