Question

A rainbow viewed from an airplane may form a complete circle. Where will the shadow of the airplane appear? Explain.

Answer 1

The position of the sun must be at the horizon in order for the rainbow to appear.
The relative positions of the sun and plane make the rainbow appear as a full circle.
However, if the sun is at the horizon, the shadow of the plane will be behind the plane, not below it; this means that the shadow of the plane will not fall on the earth.