Rainbows And How They Work

What It Covers

Rainbows form through refraction, dispersion, and internal reflection of sunlight in water droplets, emerging at precise angles of 40–42 degrees. The episode traces rainbow science from Aristotle through Newton and explores cultural mythology across eight world traditions.

Key Questions Answered

• •Rainbow geometry: Red light exits raindrops at exactly 42 degrees from the antisolar point while violet exits at 40 degrees, which is why red always appears on the outer edge and violet on the inner edge — a fixed, predictable optical law.
• •Double rainbow mechanics: A second internal reflection inside the raindrop produces secondary rainbows at 51–54 degrees from the antisolar point. This extra bounce makes them dimmer, wider, and color-reversed — red on the inside, violet on the outside — compared to primary rainbows.
• •Full-circle rainbows: Rainbows are geometrically complete circles, not arches. The horizon blocks the lower arc from ground level. Observers in aircraft or at sufficient elevation can see a nearly complete circular rainbow centered on the antisolar point directly opposite the sun.
• •Scientific progression: Descartes mathematically confirmed the 42-degree exit angle using a water-filled flask in the 1630s. Newton then proved white light contains all colors using a prism, establishing that raindrops separate pre-existing wavelengths rather than generating colors themselves.