Planetary Size Comparisons

Materials (one of each):
Basketball
Volleyball
Softball
Baseball
Standard trackball from a computer Mouse (non-optical)
Marble
Large pea
Un-cracked peppercorn

Procedure:
Show students the mouse trackball, saying that this will be your representation of Earth. Then, ask the students to try to imagine a common object that would be the size of Jupiter, as compared to the given size of Earth. Record this prediction on the board. Continuing, ask the students to think of a common object that would be the size of Saturn. Record this prediction. Continue in this manner, asking for predictions of planets in descending size-order (do not reveal that this is descending size order) - Uranus, Neptune, Earth, Venus, Mars, Mercury, Pluto. Once all planets have been predicted, reveal to the students the actual size comparisons:

Jupiter = basketball
Saturn = volleyball
Uranus = softball
Neptune = baseball
Venus = almost same as Earth (trackball)
Mars = marble
Mercury = pea
Pluto = peppercorn

After the students are able to gain a good visual comparison of the planets, ask them one final question: On this size scale, how big is the Sun? Allow the students to hypothesize, then reveal to them that the Sun would be a sphere with an 8ft. diameter.