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:
“When the shadow of death blots out my joy
And erases the face of the sun
Give me strength to endure, hope to believe
That living and dying are one.”
—William L. Wallace (20th century)
“The gods worship a line-drawing
Of a woman, in the shadow of the sea
Which goes on writing.”
—John Ashbery (b. 1927)
“We saw one schoolhouse in our walk, and listened to the sounds which issued from it; but it appeared like a place where the process, not of enlightening, but of obfuscating the mind was going on, and the pupils received only so much light as could penetrate the shadow of the Catholic Church.”
—Henry David Thoreau (1817–1862)