South Polar Halo

When Sunlight reflects and refracts off of tiny ice crystals in the atmosphere, the result can be ice crystal halos, which are related to rainbows (the latter being produced when Sunlight reflects and refracts from water droplets).
In Antarctica the temperatures are cold and the air is dry, so snow crystals grow very slowly. This slow growth tends to produce very clean hexagonal prisms, which are well suited for producing beautiful atmospheric displays. The example here is a South Pole halo, showing a rich variety of arcs and halos.
Halos arise from the way minute ice crystals in the atmosphere scatter Sunlight (or Moonlight!) into different angles.
The quality of a halo depends on the type and quality of the ice crystals that produce it.