Shadow

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 torrent of the reaching shade
    Broke shadow into all its parts,
    What then had been of shadow made
    Found exigence in fits and starts....
    Allen Tate (1899–1979)

    Beneath the sun’s rays our shadow is our comrade;
    When clouds obscure the sun our shadow flees.
    So Fortune’s smiles the fickle crowd pursues,
    But swift is gone whenever she veils her face.
    Ovid (Publius Ovidius Naso)