10 most difficult optical il­lu­sions riddles

The Fata Morgana occurs because rays of light are bent when they pass through air layers of different temperatures in a steep thermal inversion, where an atmospheric duct has formed. It significantly distorts the object on which it is based, often such that the object is completely unrecognizable. The Fata Morgana may be seen on land or at sea, in polar regions, or in deserts. It may involve almost any kind of distant objects, including boats, islands, and the coastline.

Rayleigh scattering, named after the British physicist Lord Rayleigh (John William Strutt), is an elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation.

This is known as Poggendorff illusion, first described in 1860. Many detailed studies of the illusion point to its principal cause: acute angles in the figure are seen by viewers as expanded.

This map of Africa is rotated so the continent shape resembles Australia.

There are two illusions associated with the Ames Room. First the room appears cubic when viewed monocularly from a special viewing point (the true shape of the room is trapezoidal). Secondly, within an Ames Room people or objects can appear to grow or shrink when moving from one corner to the other.

The effect is similar to irisation. Iridescent clouds are a diffraction phenomenon caused by small water droplets or small ice crystals individually scattering light. Larger ice crystals do not produce iridescence, but can cause halos, a different phenomenon.

Both shapes are the same, but the bottom one is placed more to the right. This is however difficult to notice. It is known as Jastrow Illusion.

This is a well known Zöllner illusion, first described in 1860. It may be caused by this impression of depth. The black lines are parallel, too!

In this Ehrenstein illusion the sides of a square placed inside a pattern of concentric circles take an apparent curved shape. But in reality, the sides are straight.

This is the well known checker shadow illusion, first published in 1995 by Edward H. Adelson, Professor of Vision Science at MIT. The area A appears darker because of its light surrounding. At the same time, area B, surrounded with dark areas, appear lighter.