The shape of an infralateral arc varies with the elevation of the sun. Between sunrise and before the sun reaches about 50° over the horizon, two infralateral arcs are located on either side (e.g. lateral) of the 46° halo, their convex apexes lying tangent to the 46° halo. As the sun reaches above 68° the two arcs unite to a single concave arc tangent to the 46° halo vertically under the sun.
Infralateral arcs form when sun light enters horizontally oriented, rod-shaped hexagonal ice crystals through a hexagonal base and exits through one of the prism sides. Infralateral arcs occur about once a year. They are often observed together with circumscribed halos and upper tangent arcs.