Good to know:
Humans have always been fascinated by rainbows. In Greek mythology, they were said to be the path of Iris, the messenger of the gods. In Norse mythology, a rainbow was a Bifröst bridge, connecting the homes of the gods and humans. Irish leprechauns are said to hide their gold at the end of a rainbow. Those are magical stories, but they are not true.
A rainbow is an arc of colored light in the sky. It is caused by sunlight refracting and reflecting from droplets of water, such as rain or mist, in the air. The colors of the reflected arc of light are always in the same order: red, orange, yellow, green, blue, indigo and violet.
How does sunlight create a rainbow? Light enters a drop of water. The drop acts as a prism, and refracts the light. This means the light is broken up into the individual colors, or spectrum, that are contained in the light. If the light enters the drop at just the right angle (about 42 degrees), the back of the drop acts as a mirror and reflects most of the light back out the front. Have you ever seen a double rainbow? They are caused when the droplets reflect the light twice. The colors in the spectrum of the second rainbow are in the opposite order from those in the first.