What is a shadow?



               A shadow is formed when light is incident on an opaque object and cannot penetrate into the space immediately beyond it. In other words, a shadow is that part of an illuminated surface which is shielded from oncoming light rays by an object through which the light cannot pass. This infers that it is a dark patch or area on the ground or on any other surface created by cutting off passage of light. 




               The extent and the shape of a shadow mainly depend on the size of the source of light. If the source of light is very small the outline of the shadow will be sharp and well-defined and their shapes will that of the object producing it. But if the source is large, the shadow will be very dark in the middle, and lighter on the outside with indistinct outlines. The dark part of the shadow is called umbra, i.e. the region of complete darkness and the lighter portion is called as penumbra region.

               The shadows cast by the sun always have a penumbra and the shape of the shadows cast varies with the position of the sun in the sky and the angle of rays. An upright pole will cast a long shadow in the morning when the sun is rising but will grow shorter with approaching noon. As the sun declines in the sky, the shadow grows longer again.

               The human shadows have often had a mystical or magical significance.