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:
“In order to be somebody you have to hold even your shadow in high regard.”
—Friedrich Nietzsche (1844–1900)
“The gods worship a line-drawing
Of a woman, in the shadow of the sea
Which goes on writing.”
—John Ashbery (b. 1927)
“O love, my love! if I no more should see
Thyself, nor on the earth the shadow of thee,
Nor image of thine eyes in any spring,—
How then should sound upon Life’s darkening slope
The ground-whirl of the perished leaves of Hope,
The wind of Death’s imperishable wing?”
—Dante Gabriel Rossetti (1828–1882)