A double rainbow occurs when sunlight is reflected twice inside a raindrop

We see colors as a reflection or refraction of light. Light bounces off different things and materials at different angles, thus giving us the entire array of colors that the human eye can see. After a rainfall, light refracting through droplets of water in the sky and angling into our eyes makes us see rainbows. At odd times, light can be refracted twice within a single water droplet. When this happens, we see two rainbows stacked on top of one another, resulting in a double rainbow.