What are mirage and looming?

Explanation

(i) Mirage is an optical illusion observed in deserts and coal tarred roads on hot day.
(ii) The refractive index of air increases with its density.
(iii) In hot places, air near the ground is hotter than air at a height. Hot air is less dense.
(iv) Hence, in still air the refractive index of air increases with height.
(v) Because of this, light from tall objects like a tree, passes through a medium whose refractive index decreases towards the ground.
(vi) Hence, a ray of light successively deviates away from the normal at different layers of air and undergoes total internal reflection when the angle of incidence near the ground exceeds the critical angle.
(vii) This gives an illusion as if the light comes from somewhere below the ground. This phenomenon is called mirage.
(viii) In the cold places, the refractive index increases towards the ground because the temperature of air close to the ground is lesser than the temperature above the surface of earth.
(ix) Thus, the density and refractive index of air near the ground is greater than at a height. In the cold regions like glaciers and frozen lakes and seas, the reverse effect of mirage will happen. Hence, an inverted mage is formed little above the surface. This phenomenon is called looming.