Highway mirage

Phantom water (and cars) on a road. The `water` is skylight refracted upward by a layer of very hot air near the road surface. As the rays from the sky in front of us go down from the cooler (and hence denser) air to the warmer (and hence less dense) air near the road surface, they are refracted upwards. This is because the index of refraction of air is proportional to its density (which, again, is inversely proportional to its temperature). The image was taken around noon. The phenomenon is called inferior mirage because it is visible below the horizon line.