Why Rainbows Are Always Circular

Why Rainbows Are Always Circular

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Although we typically see rainbows as arcs, they are actually full circles. The reason we usually see only a semi-circular arc is that the ground blocks the lower half of the rainbow. A rainbow forms when sunlight is refracted, internally reflected, and dispersed inside water droplets in the atmosphere, creating a circular path of light. When viewed from a high vantage point, such as an airplane or a tall mountain, it is sometimes possible to see a full-circle rainbow without obstructions. Pilots and skydivers often report witnessing this incredible sight, which reveals the true shape of rainbows.

The size of a rainbow depends on the angle at which light exits the raindrops. Typically, the primary rainbow forms at an angle of about 42 degrees from the observer’s line of sight, while a secondary rainbow appears at 50-53 degrees due to the second internal reflection. The circular nature of rainbows is a result of uniform light refraction occurring at the same angle in millions of raindrops, creating a continuous loop of color. This phenomenon highlights the fascinating way in which light and geometry work together to produce one of nature’s most mesmerizing displays. Shutdown123