Explore Rayleigh scattering interactively: see why the sky is blue at noon and turns orange-red at sunset. The inverse fourth-power law I ∝ 1/λ⁴ drives the colour of daylight.
Rayleigh scattering occurs when light interacts with particles much smaller than its wavelength (air molecules). The scattering intensity follows 1/λ⁴: blue light (450 nm) scatters ~5.5× more than red (700 nm). At sunset, longer path lengths scatter all blue light away, leaving red.
Move the sun position from noon to sunset. Watch the sky gradient change from blue through orange to deep red. The wavelength bar chart shows scattering intensity for each colour.
Lord Rayleigh published his scattering theory in 1871. The same physics explains why Mars has a butterscotch sky, why blue eyes appear blue (structural colour, not pigment), and why distant mountains look blue.