A short history of the rainbow

The history of the rainbow is as old as that of science. The ancient Greek philosophers tried to describe the rainbow, and Aristotle was the first to fully include it among the phenomena studied by physicists. Sunlight reflected in the clouds, the incidence of light rays, the reason for the rainbow’s circular shape, the optical effect of an infinite depth are aspects that have for centuries intrigued scholars, who studied the rainbow with a mixture science and alchemy, sense and sensibility. In the 17th century the rainbow became a strictly physical phenomenon, the object of rigorous investigations according to the law of reflection and refraction. Here we survey this often forgotten history, from ancient Greeks to modern scientists, the rainbow’s colours belonging to the world of physics but also—as Thomas Young wrote in 1803—to the world of speculation and imagination.