A shadow is created when an object blocks light. If the object is opaque (not letting light through not transparent like a person or a tree) it will completely block the light and form a dark shadow. If the object is translucent (not completely clear or transparent but clear enough to allow light to pass through like a tissue) it only partially blocks light. The light that does travel through scatters and creates a faint shadow. Transparent objects (able to be seen through like glass) can’t create a shadow because light passes right through them.