The Parghelia is a special case of another optical illusion — halo, which is observed in the sun, the moon and even the powerful streetlights: usually halo has the appearance of a luminous ring around the light source, but may take the form of a cross, sun pillar, or to be like a rainbow. Cause halo is a refraction of light in ice crystals that are contained in Cirrus clouds at an altitude of 5-10 km from the location of the crystals depends on how it will look like halo.
One of the known forms of the halo — 20-degree Parghelia, bright spots with two sides from the Sun at its height at an angle of 20 from him. Crystals in the form of ice plates can contribute to the emergence of secondary Parhelia at the same height, but at an angle 40 from the Sun.
Another type — 120-degree Parghelia — parheliacal point on the circle at an appropriate distance from the Sun.
There is also a Parghelia of Liliequist that occur when the crystal prisms in the clouds are horizontally — is a thickening parheliacal circle at 150-160 from the sun, and called them by name, the Swedish meteorologist, the first time they recorded.