A mirage is not real

The mirage is when you think you see an image, but it disappears as you approach it. It must not, however, be confused with hallucination, since we can very well observe it at several at the same moment and can even be photographed. The mirage is actually the deformation of an image that exists beautiful and well. It is caused by variations in temperature at ground level. The puddle you thought you saw on the road is none other than the reflection of heaven.
The mirages have fascinated man ever since their mystery and beauty. They have been the subject of many legends more or less frightening during the last centuries, but their formation is now well known and resides in the succession of several physical principles.
If one day you walk in the desert and you see an expanse of water, beware, it is perhaps a mirage ...

 

A mirage is real and that's not because of you're hallucinating, but rather it is formed by real optical phenomenon of light refraction. This is not to be confused with formation of rainbow, as it is caused by refraction of sunlight by droplets of rain water. In that case, a mirage is formed by the refraction of existing object, far far away located out of your field of view. However, in most cases, it's always due to hallucination especially when you're crossing the desert in extremely exhausted and dehydrated conditions. I haven't cross the desert myself, but I can assume what they sees are what they yearn for- Water and Food. And thus their imagination goes wild. But, should they encounter a mirage in a healthy and sane state of mind, they will be able to view what the mirage has to offer. It can be an actual oasis, a settlement, a wall, or even a town.

 

Anything that exists in the mind, real or not, as so long as it exists..it is very much real in some dimension of our timeline. What seems not to be real is as real as the breath you breath but cannot see it.