10 most difficult il­lu­sions riddles

Halo is the name for a family of optical phenomena produced by light interacting with ice crystals suspended in the atmosphere. Halos can have many forms, ranging from colored or white rings to arcs and spots in the sky. Among the best known halo types are the circular halo (properly called the 22° halo), Other common optical phenomena involving water droplets rather than ice crystals include the glory and the rainbow.

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.

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.

This is Australia map, with north at the bottom side.

A Hybrid Image is an optical illusion developed at MIT in which an image can be interpreted in one of two different ways depending on viewing distance. In order to see Marylin clearly, you need to move away of the screen