Mirage is an optical illusion created by total internal reflection of light Under normal circumstances the density of air is uniform on tar roads and hence light travels in straight line. The air layer in contact with earth gets heated up and becomes rare when compared to the upper strata of atmosphere.
Light coming from the distant objects is total internally reflected. This creates an illusion of reflection in water. The inverted image caused due to the hot air volume below is responsible for this. This phenomenon is rare in case of positions above the level of the observer.
