Common principles behind rainbows and boat wakes

Rainbows and boat wakes may seem unrelated, but they share deep mathematical connections through ray folding, caustics, and Airy interference. This paper explores these principles, which are also relevant for explaining phenomena such as shimmering effects on the bottom of pools and twinkling stars. By revisiting Airy's theories on wavefronts and caustics, we demonstrate their applications not only in optics and for water waves but also in quantum wave packets. Using concepts from undergraduate physics, we highlight the universal patterns that unify these diverse phenomena.