History of Rainbow Mystery

Rainbows were puzzling long before they became a textbook optics example. The main question was simple to ask and hard to answer: why do colors appear in a fixed arc, and why do they show up at all?

Early explanations mixed geometry, philosophy, and observation, often without a clean physical mechanism. That history is useful because it shows exactly which parts of the problem are intuitive and which parts require a more careful optical model.

This post will trace that path from descriptive accounts to the first explanations that tied the rainbow to refraction, reflection, and the geometry of droplets.