A halo in the form of an arc tangent to a circular halo. The most common of these are the upper and lower tangent arcs to the halo of 22°. They form separate arcs when the sun is low, but as the sun climbs they join to produce the circumscribed halo. These arcs are explained by refraction through the 60° prism sides of columnar crystals oriented with their long axes horizontal. See 46° lateral arcs.