Optics principles. For example, the Ames room, Hering, Müller-Lyer, Orbison, Ponzo, Sander, and Wundt illusions all rely on the suggestion of the appearance of distance by using converging and diverging lines, in the same way that parallel light rays (or indeed any set of parallel lines) appear to converge at a vanishing point at infinity in two-dimensionally rendered images with artistic perspective. This suggestion is also responsible for the famous moon illusion where the moon, despite having essentially the same angular size, appears much larger near the horizon than it does at zenith. This illusion so confounded Ptolemy that he incorrectly
Parallel (geometry) same three-dimensional space that do not intersect need not be parallel. Only if they are in a common plane are they called parallel; otherwise they are called skew lines. Two distinct lines "l" and "m" in three-dimensional space are parallel if and only if the distance from a point "P" on line "m" to the nearest point on line "l" is independent of the location of "P" on line "m". This never holds for skew lines. A line "m" and a plane "q" in three-dimensional space, the line not lying in that plane, are parallel if and only if they