Rainbows caused by sunlight always appear in the section of sky directly opposite the sun, but originate no further than 42 degrees above the horizon for observers on the ground. To see them at higher angles, an observer would need to be in an airplane or near a mountain top since the rainbow would otherwise be below the horizon.

The bigger the water droplets which form the rainbow, the brighter the rainbow will be.

A secondary rainbow can also form this rainbow is caused by light being reflected once in droplets of water. In a double rainbow, a second arc may be seen above and outside the primary arc, and has the order of its colours reversed (red faces inward toward the other rainbow, in both rainbows). This second rainbow is caused by light reflecting twice inside water droplets. 

Rainbows appear in seven colours because water droplets break white sunlight into the seven colours of the spectrum (red, orange, yellow, green, blue, indigo & violet)

On a very rare occasions you can also get a 3rd and 4th Rainbow.