A variety of optical light effects can occur in the sky.
In contrast to the rainbow, the sunlight is not refracted by raindrops in halo phenomena, but by ice plates, which are mainly found in high and therefore particularly cold clouds, the so-called cirrus clouds. The different forms of appearance within the extended Halo family are as diverse as the geometric shapes of the crystals.
In addition to the shapes of the ice crystals, which can range from hexagonal plates and cylinders to pyramid-shaped polygons, their size and orientation are also decisive for the way in which the light is refracted in them and thus broken down into its spectral colors. The position of the sun also plays a crucial role.
Halos can form a ring around the sun in different radii and frequencies, appear as spots in the form of parhelia, or reach through the sun as lines of light columns. Another special shape is the so-called circumzenith arc, which is aligned in a circle around the zenith, i.e. around the highest point in the sky.