Rainbows occur when sunlight is refracted by water droplets. From the ground, a person only sees part of a rainbow. In reality, a rainbow is in the form of a complete circle rather than the arc most people are accustomed to.
The more rain droplets that are in the air, the more colorful the rainbow will be. This is because as the light from the sun enters a raindrop, one specific color from the spectrum exits. If there are only a few raindrops, only a very faint rainbow will appear, if one appears at all. The best time to catch a bright rainbow is after a heavy downpour.
A person should stand with the sunlight at his or her back and the rainclouds off in the distance, following the direction of the body's shadow. The best time of day to see a rainbow is before 8:30 in the morning or after 4:30 in the afternoon.
On occasion, one can see a double rainbow. This is when a smaller rainbow appears within the arc of the larger one. A double rainbow is made when the water droplets reflect the light twice, instead of just once. The reflected light comes out at a different angle, which makes a secondary rainbow. For example, the red primary color is refracted at both 42 degrees and 50 degrees in a double rainbow.