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:
“At middle night great cats with silver claws,
Bodies of shadow and blind eyes like pearls,
Came up out of the hole, and red-eared hounds
With long white bodies came out of the air
Suddenly, and ran at them and harried them.”
—William Butler Yeats (1865–1939)
“Character is like a tree and reputation like its shadow. The shadow is what we think of it; the tree is the real thing.”
—Abraham Lincoln (1809–1865)
“No sooner is your ocean filled, than he grumbles that it might have been of better vintage. Try him with half of a Universe, of an Omnipotence, he sets to quarrelling with the proprietor of the other half, and declares himself the most maltreated of men. Always there is a black spot in our sunshine: it is even as I said, the Shadow of Ourselves.”
—Thomas Carlyle (1795–1881)