A Rainbow is an optical occurrence caused by the reflection of light in droplets of rain in the atmosphere. This results in the spectrum of colors we call the "Rainbow". It is the shape of an arc and is opposite the Sun.
Rainbows do not have specific location, it is actually impossible to find the end of a rainbow. It comes from light being reflected at 42 degrees, opposite the sun in any water droplet. A rainbow spans into a spectrum of colors. The colors that are most pronounced are red, orange, yellow, green, blue, indigo and violet. Rainbows can be caused by any form of water in the air not just rain.
Rainbows can be seen when there are water droplets in the air, the sun behind and at a low altitude angle. Some spectacular rainbows can be seen around waterfalls or fountains.
FUN FACT! :
Moon-bows actually exist! From the light of the moon a rainbow can be seen. However the human eye would only see the moon-bow as a white color
When the light enters the raindrop it is both refracted and reflected. It is refracted when the light enters the droplet. It then hits the back of the droplet and is reflected at an angle of 42 degrees. Here the light disperses into the spectrum and is refracted once more when it leaves the droplet. This forms a rainbow. It is in an arc shape but when viewed from above it looks like a halo.
A rainbow has no definite location. Even if one observer is looking at another who seems to be at the end of the rainbow, the second observer views the rainbow further away.
Multiple rainbows are created by reflecting the first rainbow.