Explore how air changes sunlight.
A shorter path through air
Direct sunlight
Scattered skylight
Incoming rays are parallel. Motion slowed down; atmosphere, Sun, and bending enlarged.
Air molecules scatter blue light more strongly than red. This is Rayleigh scattering. Blue light reaches you from across the sky; near sunset, a longer path through air scatters more blue out of the direct beam, leaving warmer sunlight. Red scatters too, just less strongly.
Even when the Sun is below your horizon, it still lights the atmosphere above you. That air scatters sunlight toward you, giving us twilight. As the Sun sinks farther, Earth’s shadow covers more of the atmosphere and the sky darkens. Near the horizon, refraction also bends direct sunlight, briefly letting you see the Sun even when it is geometrically below the horizon.
A teaching illustration of Earth-like air, not a calibrated simulation. Atmosphere thickness is exaggerated; clouds, dust, and weather are not modeled. Refraction is an approximate illustration, not a prediction of sunset time.