Witnessing the history, throughout the ages, mankind has always been fascinated by rainbows. And their arched splashes of color have been the subject of numerous songs and poems, stories and mythology. Even, in the Bible, the rainbow is seen as a sign of God's promises.
What makes rainbows so mysterious is the simple but often puzzling fact that rainbows are light and they exist only in the eyes of the beholder! To unlock this amazing secret of the nature and explore how water and light work together to produce the magnificent colorful work of art, we have to understand a little bit of physics, because that’s what it is – pure science!
You need three factors to work together to see a rainbow. Firstly, the sun must be shining. Secondly, the sun must be behind you, and thirdly, the air in front of you must have water drops in it. When the sunlight enters a water drop, it is refracted, or bent, and reflected out from the drop in such a way that the light appears as a spectrum of colors. Actually, the rays of light bend twice. As they enter the drops, the rays of light bend, then reflect off the back of the drops. Then they bend again, this time while exiting the drops. That's when the light appears before our eyes. Each drop reflects only one color of light, so there must be many water drops to make a full rainbow. You'll see the brightest rainbows when the water drops are large, usually right after a rain shower.
When a raindrop bends light, the light exits the raindrop at an angle of 40 to 42 degrees away from the angle it entered the raindrop. As a result, the only beams of light you see are from raindrops that are 40 to 42 degrees away from the shadow of your head. This gives the rainbow its curved appearance.