Explain where the sun and the rain are when a rainbow occurs. The sun is always behind you while the rain is in the direction of the rainbow.
Talk about the reasons why the rainbow forms a bow shape. Explain that the light is refracted when it hits the spherical raindrops, and then it becomes reflected within the drop before being refracted once again as it leaves the drop of rain. Since this is happening with so many drops at once, it forms a bow.
Explain that the colors of the rainbow come from the sun, which is actually filled with the entire spectrum of colors at all times. It is normally impossible to see any colors but white. When the light is refracted through the raindrops, the colors separate. The rainbow consists of the colors red, orange, yellow, green, blue, indigo and violet. It actually has more colors that human eyes are not able to see.
Talk about how rainbows can also be made with mirrors, water and sunlight. If you place a mirror in water and tilt it towards the sun, you can create tiny rainbows on a nearby wall or blank sheet of paper.
Explain that a double rainbow occurs when the light is refracted through more than one layer of raindrops. This creates the visual effect of a double rainbow, which is a rare occurrence.