Blue Sky
Air molecules scatter short-wavelength (blue/violet) light in all directions. You see scattered blue everywhere except toward the sun.
Module 04
Scattering of Light & the Sky
Air molecules scatter shorter wavelengths far more than longer ones. That single fact explains a surprising amount of what you see in the sky.
Atmosphere Simulator
Sun noon
Sun elevation72°
At noon (high sun), light takes the shortest path — the sky looks light blue/white. Near sunset, the path is long: most blue is scattered away, leaving the red end to reach you.
Rayleigh Intensity
Probe wavelength450 nm
Scattered intensity ≈ 2.23× green.
Atmospheric Phenomena
Red Sunrise / Sunset
At the horizon, sunlight travels a long path. Blue is scattered out; only red reaches you directly.
White Sky at Noon
Shortest atmospheric path — little selective scattering — direct light looks nearly white.
White Clouds
Water droplets are larger than the wavelength of light — they scatter all colours equally.
Black Sky on the Moon
No atmosphere means no scattering. Away from the sun, the sky is black.
Astronaut's View
Earth looks blue (scattered sunlight from its atmosphere) against the black sky of space.
Why are danger signals red?
Red light has the longest visible wavelength, so it is scattered the least — it travels farther through fog, smoke and dust.
Red 680 nmreach: 100%
Green 510 nmreach: 31%
Blue 450 nmreach: 19%