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 whole shadow of Man is only as big as his hat.”
—Elizabeth Bishop (1911–1979)
“It was a favor for which to be forever silent to be shown this vision. The earth beneath had become such a flitting thing of lights and shadows as the clouds had been before. It was not merely veiled to me, but it had passed away like the phantom of a shadow, skias onar, and this new platform was gained. As I had climbed above storm and cloud, so by successive days’ journeys I might reach the region of eternal day, beyond the tapering shadow of the earth.”
—Henry David Thoreau (1817–1862)
“I have a little shadow that goes in and out with me,
And what can be the use of him is more than I can see.
He is very, very like me from the heels up to the head;
And I see him jump before me, when I jump into my bed.”
—Robert Louis Stevenson (1850–1894)