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Greek mythology would say that he appears whenever the goddess Iris leaves a colored trail in the sky, to convey to men the messages of Zeus, the almighty one of Olympus. The scientific explanation is far less romantic. The rainbow appears when the Sun illuminates the moisture suspended in the air, after a downpour, for example. When lightning hits the edge of a drop of water or steam, the white light of the Sun is deflected and breaks down into the seven colors that make up its spectrum: red, orange, yellow, green, blue, indigo and violet. It’s the same prism effect we learned in school: each color is reflected at a different angle and changes direction as it returns to the atmosphere. The red color propagates the fastest, forming the upper band of the rainbow. Violet, the slowest, appears at the bottom.
The phenomenon is so common that scientists have amassed some colorful records. “In the laboratory, more than 12 rainbows were observed from a single drop of water”, says physicist José Pedro Rino, from the Federal University of São Carlos (UFSCAR).
natural prism
1. Inside the drop of water or steam, the sun’s ray undergoes refraction – that is, it is divided into the seven colors that make up white light
2. Each colored wave is deflected at a different angle according to the smooth speed of propagation
3. The colored rays are reflected from the bottom edge of the drop
4. As they exit the drop, the rays are deflected once more. The effect is like that of a magnifying glass.
5. The show ends when the sun changes position or when a strong wind dissipates moisture from the air.
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