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. And if we happen to take our walk closer to sunset, our shadows are longer than if we go out in mid-afternoon. What makes shadows act this way?