What will be the ideal response?
ANSWER: Occasionally, a bright arc of light may be seen at the top of a 22° halo. Since the arc is tangent to the halo, it is called a tangent arc. Apparently, the arc forms as large six-sided (hexagonal), pencil-shaped ice crystals fall with their long axes horizontal to the ground. Refraction of sunlight through the ice crystals produces the bright arc of light. When the Sun is on the horizon, the arc that forms at the top of the halo is called an upper tangent arc. When the Sun is above the horizon, a lower tangent arc may form on the lower part of the halo beneath the Sun. The shape of the arcs changes greatly with the position of the Sun.
Beautifully done! Thanks