How Waterfalls Create Rainbows

Rainbows at waterfalls form through the same optics as rainbows in rain—refraction, reflection, and dispersion of sunlight in water droplets.

Step-by-Step Process

1. Sunlight enters a spherical water droplet from the waterfall's mist.
2. Refraction at the air-water interface bends light; shorter wavelengths (violet) bend more than longer (red).
3. Internal reflection off the droplet's back surface.
4. Second refraction on exit further separates colors.
5. The dispersed light forms a circular arc centered on the antisolar point (shadow of your head).

Key Conditions

• Sun behind you, mist in front.
• Sun angle ~42° above horizon (rainbow radius = 42°). Best seen early morning or late afternoon.
• Droplet size – Waterfall mist provides ideal 0.1–1 mm droplets.

Famous Waterfall Rainbows

• Yosemite Falls (spring) – "moonbows" on full-moon nights
• Niagara Falls – persistent mist clouds
• Victoria Falls – "The Smoke That Thunders" creates massive rainbows
• Skógafoss, Iceland – frequent double rainbows

Each observer sees their own unique rainbow—no two people share the exact same set of droplets.