Sundials have been used since ancient times to measure the time by the angle of the shadow a stationary object casts. Help students construct sundials by sticking a pencil up through the center of a paper plate, then weigh the sundials down with rocks in a sunny spot outside. Check the sundials every hour and make a mark on the plate to show where the shadow falls at that time. A fun variant is to have a child stand in the same spot every hour and let a partner mark the tip of his shadow with a rock.
The real question behind Groundhog's Day is whether the weather will be sunny or overcast at that point in the year, since shadows are visible on sunny days but not in gray weather. In the weeks leading up to Groundhog's Day, children can observe and chart the weather patterns to see whether they can predict whether a groundhog will be able to see its shadow. As an alternative, kids can chart temperature in the weeks after Groundhog's Day to see whether the groundhog's prediction was correct.
Tracing shadows can engage kids with the theory of shadows in a concrete, active way. Give each child a stick of sidewalk chalk and let them take turns tracing each others' shadows on a pavement or parking lot. Discuss the similarities and differences between a person and her shadow, such as the fact that a shadow only shows the person from one angle and that it can be taller or shorter. Help children make the connection between the position and the sun and the length of their shadows.
This experiment helps children learn about how different colors of light and shadow interact. Set up two or more lights with different colored filters, such as red, blue and yellow. Place the lights in an arc, pointing at the same spot on a white screen but positioned about 30 degrees apart from each other. Let children stand in front of the screen and try to cast shadows of different colors. Other kids can act as assistants and block or turn off different combinations of lights to help achieve new colors.