Perspective, in context of vision and visual perception, is the way in which objects appear to the eye based on their spatial attributes; or their dimensions and the position of the eye relative to the objects. There are two main meanings of the term: linear perspective and aerial perspective.
The development of new forms of geometric projection in the construction of perspective corresponds with the invention of novel pictorial art forms of visual representation in the Italian Renaissance, since the fourteenth century and up till the end of the sixteenth century, and specifically within the circles of architectural and artistic experimentation and design. Treatises were composed on perspective by eminent theorists of art and architecture, including figures like Leon Battista Alberti, Lorenzo Ghiberti, and Piero della Francesca, aided also by experimental uses of optical devices through the installations of Filippo Brunelleschi. The investigations and writings of these Renaissance theorists of architecture and visual art were informed by the studies in classical optics of thirteenth-century Franciscan perspectivists like Roger Bacon, John Peckham, and Witelo, who all were directly inspired and influenced by the translation into Latin from Arabic of the Book of Optics (known in Latinate renditions as Perspectiva, and in Arabic as Kitab al-manazir) of the eleventh-century Arab polymath and optician, Alhazen (Ibn al-Haytham).
A shadow is an area where direct light from a light source cannot reach due to obstruction by an object. It occupies all of the space behind an opaque object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, or reverse projection of the object blocking the light. The sun causes many objects to have shadows and at certain times of the day, when the sun is at certain heights, the lengths of shadows change.
An astronomical object casts human-visible shadows when its apparent magnitude is equal or lower than −4. Currently the only astronomical objects able to produce visible shadows on Earth are the sun, the moon and, in the right conditions, Venus or Jupiter.