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:
“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)
“Suddenly I’m not half the girl
I used to be.
There’s a shadow hanging over me . . .
From me to you out of my electric devil....”
—Anne Sexton (1928–1974)
“You survived because you were the first.
You survived because you were the last.
Because alone. Because the others.
Because on the left. Because on the right.
Because it was raining. Because it was sunny.
Because a shadow fell.”
—Wislawa Szymborska (b. 1923)