Why the Sky Is Blue and What Trees Have to Do With It

When I started learning fiber optics, I didn't expect to understand the sky better. But the physics of light in glass — Rayleigh scattering, wavelength dependence, total internal reflection — turns out to be the same physics that governs every sunbeam through a forest or painting the horizon red at dusk.

The sky is blue because of Rayleigh scattering: light scatters off air molecules in proportion to 1/λ⁴, meaning shorter blue wavelengths scatter roughly 5–10 times more than longer red wavelengths. The same mechanism is at work in your fiber. Glass isn't perfectly uniform — microscopic density fluctuations scatter the signal, and shorter wavelengths scatter more. That's why 1550 nm performs better than 1310 nm over long spans, and why the sky isn't violet. When sunlight travels through a longer path at sunset, all that extra atmosphere scatters away the blue light before it reaches you, leaving orange and red. And when white light passes through leaves, chlorophyll absorbs red and blue for photosynthesis while reflecting green — the same way a fiber with a dirty connector will let some wavelengths through while blocking others. Light is light, whether it's traveling through 8,000 miles of atmosphere or 50 kilometers of G.652 fiber.