Anthelion

An anthelion (plural anthelia, from late Greek ανθηλιος, "opposite the sun") is a rare optical phenomenon appearing on the parhelic circle opposite to the sun as a faint white halo, not unlike a sundog.

How anthelions are formed is disputed. Walter Tape, among others, has argued they are not separate haloes, but simply where various haloes caused by horizontally oriented column-shaped ice crystals coincide on the parhelic circle to create a bright spot. If this theory is correct, anthelia should only appear together with these other haloes.