Why are mirages caused

Mirages really have nothing to do with water at all. Normally, light waves from the sun travel straight through the atmosphere to your eye. But, light travels at different speeds through hot air and cold air. Mirages happen when the ground is very hot and the air is cool. The hot ground warms a layer of air just above the ground. When the light moves through the cold air and into the layer of hot air it is refracted bent. A layer of very warm air near the ground refracts the light from the sky nearly into a U-shaped bend.

There might not even be mountains there at all. Mirages are most common in deserts. They happen when light passes through two layers of air with different temperatures. The desert sun heats the sand, which in turn heats the air just above it. The illusion comes from the fact that quantum electrodynamics is not intuitive and the human brain assumes that light travels in a straight line.

A viewer looking at, say, the road ahead on a hot, still, day will see the sky because photons from the sky are taking the curved path that minimizes the time taken. The brain interprets this as water on the road because water would reflect light from the sky in much the same way that a vertical temperature gradient does. A simple experiment can demonstrate the manner in which a light beam bends in a vertical density gradient.

Fill a long glass tank with water, dissolve sugar in the water and shine a laser beam in one end. The vertical gradient produced by the sugar concentration will cause the beam to bend. If the tank is long enough and a mirror is placed on the bottom, the beam will "bounce" along the bottom of the tank.

Originally published on November 17, As a result, the observer sees the object and its image reflected on the ground. This leads him to think, if he finds himself in the desert, that there is a mass of water that gives rise to this reflection, or a wet area on the pavement if he is driving along the road; both disappear when reached.

The mirage of ghost ships sailing across the clouds on the northern coasts is also common. This is the Fata Morgana effect.