A halo in the form of arcs that pass both obliquely and vertically through the 22° parhelia. The arcs of Lowitz are explained by refraction through the 60° prism of hexagonal plate ice crystals, oscillating as they descend. The principal axis of the plate must oscillate about the vertical by less than 30° to produce the pattern customarily called Lowitz arcs; larger oscillations lead to more complex arcs spreading far above and below the 22° parhelia and halo. See parhelion.