Shadow

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, the planet Venus.

Read more about Shadow:  Variation With Time, Non-point Source, Shadow Propagation Speed, Color of Shadow On Earth, In Photography, Fog Shadows, Other Notes, Mythological Connotations, Heraldry

Famous quotes containing the word shadow:

    The shadow of the Venetian blind on the painted wall,
    Shadows of the snake-plant and cacti, the plaster animals,
    Focus the tragic melancholy of the bright stare
    Into nowhere, a hole like the black holes in space.
    John Ashbery (b. 1927)

    Nor now the long light on the sea—
    And here face downward in the sun
    To feel how swift how secretly
    The shadow of the night comes on . . .
    Archibald MacLeish (1892–1982)

    A perfect beauty of a sunflower! a perfect excellent lovely sunflower existence! a sweet natural eye to the new hip moon, woke up alive and excited grasping in the sunset shadow sunrise golden monthly breeze
    Allen Ginsberg (b. 1926)