Rainbows... Beautiful but what are they? Rainbows are raindrops and sunlight interacting in the perfect way. Just like a prism, light hits a drop of water and forms brilliant colors. White light enters a raindrop which has a different density than the surrounding air. Due to the changes in density, raindrop density compared to the density of air, the speed of the light changes. The change in speed causes the light to bend (angle of refraction). The light bends as it enters the raindrop (refraction) and then reflects off the back of the raindrop. When the light leaves the raindrop, the light speeds up and bends again (refraction). It is the two refractions, that are not parallel, that cause the light to break up into a spectrum of colors.    Read more »