did you know a hot road can borrow a piece of the sky?

that watery-looking patch on a hot road may be an inferior mirage. light from the sky bends through layers of differently heated air and reaches your eyes from a direction that appears to be below the horizon.

there need not be any. your visual system interprets incoming light as travelling along a straight line. when the actual path curves, the apparent location of its source can be misleading.

air close to a hot surface can be warmer and less dense than the air above. its refractive index is lower. a ray travelling through that gradient can curve upward towards an observer.

tracing its final direction backward makes it appear to come from the road. because it carries sky light, it resembles a reflection from a puddle.

Snell's law describes how direction changes between layers with different refractive indices. a smooth atmospheric gradient acts like many tiny changes rather than one sharp glass-like boundary.

n₁ sin θ₁ = n₂ sin θ₂, with angles measured from the normal

• the viewing geometry changes as you move. the rays that reach your eyes no longer trace back to the same apparent patch.
• a different temperature layering can create superior mirages, making distant objects appear raised or distorted. the direction of the gradient matters.