Upper Tangent Arc and Sun Pillar
April 04, 2003
The photo above was taken ove southern Ohio and shows part of a halo display, which was captured one evening early last month. When the Sun neared the horizon, a beautiful upper tangent arc formed (near the top of the photo). Note its "V" or "U" shape and that the vertex of the "V" points toward the Sun. The appearance of this arc may vary considerablly, depending upon the elevation of the Sun. Pencil shaped hexagonal crystals, with their long axis horizontal to the surface, are responsible for the formation of this type of arc. A Sun pillar and faint 22 degree halo are also visible on the photo. While not shown on the picture, a supralateral arc and extended parhelia (Sun dog) was also observed during this halo display.