Rainbows are always opposite the Sun and their centres are below the horizon at the the so called antisolar point. Early morning and late afternoon it the best time to see a rainbow because the sun must not be too high. The lower the sun the higher is the rainbow.
In this photo I took in Vansbro, Sweden, taken just before sunset, the rainbow is as high as it gets and with the reflection in the water, acting as the lower half of a circle, it's easy to see that the rainbow was at its highest position. Had the Sun been any higher in the sky, this circle had been more ellipse shaped.
Rainbows are rarer than might be thought, halos are much more common.