2D Why Is the Sky Blue: Rayleigh Scattering

This is the flat companion to the 3D blue-sky simulator: instead of an orbitable dome, it renders the sky as a simple gradient panel driven by the same Rayleigh-scattering physics — scattered intensity proportional to 1/λ⁴. Drag the sun-elevation slider from overhead down to the horizon to see the zenith stay deep blue while the sun and the sky around it shift from white through gold to red as the slant path through the atmosphere lengthens. The particle-density slider scales how much air the light passes through, and the live chart shows exactly how much more strongly short wavelengths are scattered than long ones at the current settings.