Rainbows are actually full circles when viewed from above, but on the ground we view them as arches that appear to touch the horizon and I started to think about how the sun come up from the horizon and arches through the sky then disappears at another point on the horizon; basically the sun and a rainbow appear the same from the ground and they are also both circles (or in the case of the sun following a circular path) in the sky above us ^_^
It is also highly likely that rainbows are a full circle because they are reflecting off of the circular dome encasing our realm ^_^
