[paul.fr]

is this the right section?

Why do people see mirages, and What is going on in the brain when one is seen?

[DoctorBeaver]

Mirages do not necessarily originate in the brain. They can be the result of heat bending light rays.

The classic mirage is seeing water in the middle of a desert. I've seen that myself. The sand near to you is matt but the effect of the heat gives the appearance of water or glass to areas of sand further away.

In some cases, though, they do indeed originate in the brain. Dehydration can have very serious effects as can overheating of the brain. I'm not certain of the physiology involved but I'm sure it can cause hallucinations.

[Karen W.]

I have never seen a mirage but I could envision a pretty handsome one !LOLIt is interesting where they really stem from.

[lightarrow]

is this the right section?
Why do people see mirages, and What is going on in the brain when one is seen?

Which kind?
One of them is "Fata Morgana".
http://en.wikipedia.org/wiki/Fata_Morgana_%28mirage%29
It's the opposite of the mirage of water in desert: in the sea, you see far ships as "flying". From which, presumably, the legend of the "flying dutch".

It's due to the fact that air just over the water can be colder than air some metres over, so light coming from a distant object is deflected down, so you see the object as if it was up.

In the case of the desert, air is hotter near the sand and colder up so light is deflected up and you see the image of the sky coming from the ground, resembling a water pond.

There are many others. For example, seeing the sun or the moon as bigger at the horizon. There has been a thread on this subject, here.