Inferior Mirage Observed from Plemmirio, Syracuse, Italy
February 12, 2021
Photographer: Kevin Saragozza
Summary Author: Kevin Saragozza
Mirages are quite common and very fascinating phenomena. Their mechanism of formation is a consequence of the laws of geometric optics, especially refraction. We can distinguish mirages into two main classes; superior (upper) mirages and inferior (lower) mirages. An example of an inferior mirage, the type most often seen, is what looks to be wet asphalt on the road ahead of us on a hot summer’s day. What we’re seeing, in fact, is nothing more than the refracted image of the sky. On the photo above, taken near Plemmirio, Syracuse, Italy, we’re able to see the distant town of Portopalo di Capo Passero floating on the horizon, even though it’s some 25 miles (40 km) away. Of course, in the absence of this inferior mirage, we wouldn’t be able to see this far.
Mirages are formed in the presence of rather intense air temperature gradients -- an abrupt temperature variation between nearby air layers. When the temperature decreases very rapidly as the height above the ground increases, the density of the air changes just as rapidly. Because of this, a light ray no longer propagates in a straight line but is bent upwards and forms a lower mirage. As a result, an object appears lower than it is in reality, hence the name inferior mirage. Photo taken on December 13, 2020 (15:49 local time).
Photo Details: Canon Eos R camera; + 70-200 2.8 lens; f9; 1/500 sec. exposure; ISO100