How are mirages formed?

Mirages are a result of refraction. They are often sighted in deserts. Some people might call it hallucination but there is a reason why there can be an “oasis” appearing in the middle of a desert when there actually in not one. I have been wondering how they are formed and I did not really understand the explanation. However, now that we have learnt on refraction, I now can relate a little better.

Mirages are formed when light rays are bent as the light ray passes through air layers with different densities. This is actually refraction. The reason why mirages can be form due to varying densities of air is because the index of refraction for air varies with the density of the air. Air density is dependent on its pressure, temperature and water vapour content. Air density is also proportional to its pressure, which means that density increases as pressure increases and it is also inversely proportional to its temperature, which means that density decreases as temperature increases.

This image is trying to express that the “oasis” that the eye apparently sees is actually a mirage. The mirage of the oasis is actually the image of the bluish sky being strongly refracted by the hot air near the surface so that it appears to be water lying on the surface. This is also known as an inferior mirage as the warm air is below the cool air.

The opposite of an inferior mirage is a superior mirage. It occurs when the cool air is under the warm air. It happens very often at sea , or over ice and snow surfaces. When cold air lies below the warm air, the light rays from the object is bent towards our eyes, tricking it into thinking that the object is higher or taller in appearance than it actually is. It can also make objects appear as though it is floating. Here are some examples:

Sources, Help and Images:
http://www.islandnet.com/~see/weather/elements/mirage1.htm