Shadow
The cross section of a shadow is a two-dimensional silhouette, or a reverse projection of the object blocking the light.
A viewer located in the penumbra region will see the light source, but it is partially blocked by the object casting the shadow.
If there is more than one light source, there will be several shadows, with the overlapping parts darker, and various combinations of brightnesses or even colors.
The absence of diffusing atmospheric effects in the vacuum of outer space produces shadows that are stark and sharply delineated by high-contrast boundaries between light and dark.
The names umbra, penumbra and antumbra are often used for the shadows cast by astronomical objects, though they are sometimes used to describe levels of darkness, such as in sunspots.
[2] The only astronomical objects able to project visible shadows onto Earth are the Sun, the Moon, and in the right conditions, Venus or Jupiter.
The length of a shadow cast on the ground is proportional to the cotangent of the sun's elevation angle—its angle θ relative to the horizon.
[6] The farther the distance from the object blocking the light to the surface of projection, the larger the silhouette (they are considered proportional).
The increase of size and movement is also true if the distance between the object of interference and the light source are closer.
[8] Visual artists are usually very aware of colored light emitted or reflected from several sources, which can generate complex multicolored shadows.
Chiaroscuro, sfumato, and silhouette are examples of artistic techniques which make deliberate use of shadow effects.
A thin fog is just dense enough to be illuminated by the light that passes through the gaps in a structure or in a tree.
In photography, which is essentially recording patterns of light, shade, and color, "highlights" and "shadows" are the brightest and darkest parts, respectively, of a scene or image.
Ancient Egyptians surmised that a shadow, which they called šwt (shut), contains something of the person it represents because it is always present.
In a commentary to The Egyptian Book of the Dead (BD), Egyptologist Ogden Goelet, Jr. discusses the forms of the shadow: "In many BD papyri and tombs the deceased is depicted emerging from the tomb by day in shadow form, a thin, black, featureless silhouette of a person.
"[11] Scientists from the National University of Singapore presented a shadow-effect energy generator (SEG), which consists of cells of gold deposited on a silicon wafer attached on a plastic film.
