This rainbow looks rather short. Why is this?
Rainbows would actually be complete circles if the light were not intercepted by the earth surface (maybe you've seen complete circle rainbows when you look at the sprinklers that water your lawn). The center of the rainbow circle is in the line of sight between the sun at your back and your eye. Rainbows will look short if the sun is high in the sky because more of the rainbow light is intercepted by the surface. When the sun is low in the sky less of the rainbow light is intercepted by the ground and you see more of the full rainbow.
An attempt to illustrate this phenomenon is shown: