- Definition: Shadows have been generated whenever an opaque item has been put inside the course of light rays.
- An opaque item is one that does not allow illumination to flow through it.
- People long ago recognized how the sun cast shadows as well as used similar ideas to create the globe's simplest basic timepieces, sundials.
- For example, the Human body - A black zone arises because illumination cannot enter through the human body. A shadow seems to be a dark zone wherein light could not penetrate.
Therefore, a black pattern produced on the ground by a body intercepting light waves from either an illumination is a shadow.