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:
“There is no shadow of protection to be had by sheltering behind the slender stockades of visionary speculation, or by hiding behind the wagon-wheels of pacific theories.”
—Madame Chiang Kai-Shek (b. 1898)
“The torrent of the reaching shade
Broke shadow into all its parts,
What then had been of shadow made
Found exigence in fits and starts....”
—Allen Tate (1899–1979)
“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)