Directions:

• Discuss with the students that they will be creating a model for the distance from the Sun and Earth to Saturn (or the entire solar system, if you wish). Talk about ways that models are useful to scientists, and also ways that models are alike and different from "real life."

• Tell the students that because distances in space are so vast, scientists have come up with some different ways of measuring these distances. One way is to use a unit called an astronomical unit. An astronomical unit is equal to the distance from Earth to the Sun (93 million miles, or 150 million kilometers).

For our model, the length of one person's foot will be one astronomical unit!

• Practice measuring the astronomical units by walking slowly, placing the heel of the foot against the toes of the other foot (some people call these "baby steps" or "heel-toes").

• Place the Sun cup or card at one end of the classroom, hallway, or outside.

• Ask students to predict (they can mark their predictions with chalk X's on the pavement if you do this out-of-doors) where they think Earth and Saturn will be, relative to the placement of the model Sun. They can also predict how many astronomical units (real feet) they think this will be.

• If you are doing this as a whole-group demo, select the student whose feet/ steps will be used for the model. Otherwise, distribute written directions (or envelopes) to partners/groups. Remind students of how to measure the astronomical units, walking heel-toe.

• Have your astronomical unit model place her or his heel against the Sun cup, or index card set in a clay ball.

Place the planets as follows:

• Mercury: instep

• Venus: big toe joint

• Earth: tip of the big toe

• Mars: 1.5 steps

• Jupiter: 5 steps

• Saturn: 9.5 steps

• Uranus: 19 steps

• Neptune: 30 steps

• Pluto: 39 steps