🔵 Rayleigh Scattering Simulator

Why is the sky blue? Why are sunsets red?

This simulation models Rayleigh scattering — the physical phenomenon where light interacts with molecules in Earth's atmosphere. The key insight is that scattering intensity is proportional to λ⁻⁴, meaning shorter wavelengths (blue/violet) scatter ~10× more than longer wavelengths (red).

The Physics

When sunlight enters the atmosphere, gas molecules scatter shorter wavelengths much more efficiently than longer ones:

• Overhead sky (short path): Blue light scatters in all directions → sky appears blue
• Sunset (long path): Blue is scattered away entirely, only red survives → sky appears red/orange

Features

• Calculate Rayleigh cross-sections for any wavelength
• Simulate sky color at any zenith angle (0° = overhead, 90° = horizon)
• Chapman-like atmospheric path length model
• Color intensity bar charts for visualization

Quick Start

python rayleigh.py

Output

The simulator shows:

1. Relative scattering intensities across the visible spectrum
2. Sky color evolution from zenith to horizon
3. Quantitative explanation of why blue drops ~5000× while red drops only ~15×

References

• Rayleigh, Lord (1871). "On the light from the sky, its polarization and colour"
• Hansen & Travis (1974). "Light scattering in planetary atmospheres"