Find a Ping-Pong ball on the next clear day when the Moon is out. Hold the Ping-Pong ball with your arm stretched out toward where the Moon is so that the ball overlaps the Moon. Look carefully at how the ball is lit by the Sun. Notice that this is the same way the Moon is lit by the Sun! For an example, see the photograph accompanying Exercise 75. To see the different phases that the Moon would have if it were elsewhere in the sky, move your Ping-Pong ball around. Note as you bring the ball closer to the Sun, the crescent on the ball gets thinner. The same thing happens with the Moon. This activity is a great way of really experiencing the roundness of the Moon.