The mirage is a kind of weather illusion and optical phenomena in which light rays are refracted to form displaced images of distant things. The term mirage has been derived originally from the French term – ‘se mirer' meaning ‘to be reflected'. It may also have been derived from the Latin word- ‘mirare', meaning 'to appear'.

Cause of Mirage

Mirages are caused due to the variations of temperature within the atmosphere of the earth. Cold air is normally denser than hot air and hence the refractive index is greater. Mirages are caused when refracted light passes through atmospheric layers and makes distant objects look closer, raised or inverted.

Types of Mirage

Usually Inferior and Superior Mirage are the most common forms of image.

The mirage is known as inferior because the image is visible under the real object. In such case for instance the real object may be the sky and the image will appear in the distance as the blue patch on the ground. This explains why the barren expanse of land suddenly appears as an oasis or a body of water to the exhausted travelers on a dry, sultry afternoon. The water body seems to disappear when they get closer to that spot. Sometimes owing to inferior mirage it also seems that oil or water has been spilled on a pitched road. These types of mirage are also known as highway or desert mirage.

When the air below the line of vision gets colder a superior mirage occurs. Temperature inversion takes within atmosphere and the rays of light bends down thus causing the image to appear above the real object. The Polar Regions are characterized by superior images. For instance the distant seashore may seem elevated with irregular spikes due to the superior mirage.