How Mirages are formed?
The most simple analogy of mirage is the reflection of the subject in calm water. We see what is called in optics "imaginary image". Water has an optical density and refractive factor other than air. It is for such a principle that Mirage arise. The condition for them is a sharp change in the optical density of air. This happens, for example, when the surface of the Earth, and hence the air layer near the surface is strongly heated with solar radiation: in the desert, where the sand temperature reaches 60-70 ° C, or sometimes above the asphalt road. Then the optical beam coming from the real object undergoes a deviation on the curve in the lower layer of air and enters the eye of the observer, which sees an inverted image of items. Imaginary image of the sky creates the illusion of water on the surface. So it arises that in the optics of the atmosphere is called the lower mirage. He is unstable, because the heated air tends to the top, the image can "swim", distort or disappear.
Less often arises upper mirage. Its condition is the presence of a strong temperature inversion in a layer above the ground – this is when the temperature with a height increases. Then the refraction of the rays occurs precisely in this heated layer and the image as it would steer over the surface. Upper Mirage is also unstable, since such an unusual temperature distribution in the atmosphere is short. An even more rare phenomenon – simultaneous conditions and for the top, and for the Lower Mirage (Fata Morgan). At the same time, rays are refracted both in the upper and lower layer. The image is distorted beyond recognition, and the observer takes an ordinary stone for a high house, a cliff – for a wonderful castle. Such a phenomenon is observed in low latitudes near the sea coast.
Very interesting optical phenomenon – refraction – arises, on the contrary, in high latitudes, in the supremor regions. Refraction is the refraction of sunlight in the atmosphere itself. Due to refractures, you can see the sun even when it went beyond the horizon! Or the refraction of the rays as if lifting the image of the shone, and the observer sees the sunrise before it actually occurs on the horizon. The reason is the same – the solar beam applies in the air not in a straight line, but on the convex curve line. This phenomenon first watched. Barents during wintering on the new land in 1596-1597. He called it "Effect of new land". Due to this effect, the polar day on the poles can be 14 days longer than the polar night, instead "Located" for half a year.
Of course, Mirage and other complex optical phenomena sometimes spent the fear and superstition. I think that not all the phenomena have studied quite in detail. Isn’t it explained by numerous "Evidence testimonies" UFO?