In rare cases a brightening can be seen opposite the sun on the parhelic circle. This white brightening is called anthelion.
The way how an anthelion is formed is still disputed. According to one opinion (Tape), an anthelion is no separate kind of halo. Rather of the contrary, the brightening forms because several halos overlap just at that point opposite the sun. These are the parhelic circle, the diffuse anthelic arcs and Tricker‘s and Wegener‘s anthelic arcs. With the exception of the parhelic circle, all these halos require column-shaped ice crystals which are orientated horizontally in an almost perfect way. According to this theory, the anthelion should be visible together with other halos caused by column-shaped crystals if the ice crystals are spread over the whole sky. But anthelia have also been observed without any other halos caused by column-shaped ice crystals. This might be a hint that anthelia are a separate kind of halo. According to Visser anthelia are caused by quadruple prisms with two vertical side faces. These reflect the light. twice from the outer prism faces and return it at an angle of 180°. Another expanation has been given by Greenler. According to him, anthelia are generated in column-shaped ice prisms which reflect the light twice inside the crystal.