To see the full circle, however, you will have to be in an airplane, literally above the clouds. Or you could create your own ...

Thus we see only the top half of the circle and are led to believe that we are seeing a semicircle rainbow. Full circle ...

If you were high up in a plane, or up a mountain, you would see a rainbow as a full circle. The next time it is a sunny day you can even create your own rainbow! If you use a water spray or hose ...