A rainbow is one of the most beautiful sights in nature, and man has long wondered what makes it happen. Even Aristotle, the great Greek philosopher, tried to explain the rainbow. He thought it was a reflection of the sun’s rays by the rain, but this was not really a complete answer.
Sunlight, or ordinary white light, is really a mixture of all the colors. You’ve probably seen what happens when light strikes the beveled edge of a mirror, or a soap bubble. The white light is broken up into different colors. We see red, orange, yellow, green, blue, and violet.
An object that can break up light in this way is called “a prism.” The colors that emerge form a band of stripes, each color grading into the one next to it. This band is called “a spectrum.”
A rainbow is simply a great curved spectrum, or band of colors, caused by the breaking-up of light which has passed thru raindrops. The raindrops act as prisms.
A rainbow is seen only during showers, when rain is falling and the sun is shining at the same time. You have to be in the middle; the sun shines over your shoulder into the raindrops, which break up the light into a spectrum, or band of colors. The sun, your eyes, and the center of the arc of the rainbow must all be in a straight line!
If the sun is too high in the sky, it’s impossible to make such a straight line. That’s why rainbow are seen only in the early morning or late afternoons. A morning rainbow means the sun is shining in the east, showers are falling in the west. An afternoon rainbow means the sun is shining in the west and rain is falling in the east.
Superstitious people used to believe that a rainbow was a sign of bad luck. They thought souls went to heaven on the bridge of a rainbow, and when a rainbow appeared it meant someone was going to die!