This example discusses the process of cloud formation and the ability of cloud droplets to scatter light. A demonstration \r\nthat creates a cloud in a beaker is described.

The dogs I know like to be walked at least twice a day -- once in the morning, and once in the evening. But even though I'm the same person and it's the same dog in the morning and evening, our shadows change... In the morning, our shadows point in one direction. This is true regardless of which way we are facing. The shadows of trees, buildings, cars, fire hydrants, and blades of grass all point in the same direction as ours. In the evening, our shadows all point in approximately the opposite direction.

When a photon ( a very small increment of energy) encounters a substance one of three things may happen. (1) The photon may be transmitted -- it passes through without alteration. (2) The photon may be absorbed -- the photon never leaves the particle. (3) The photon may be scattered -- it's path may be altered.