Make a 0.9-inch ball of red modeling clay, a 0.7-inch ball of yellow modeling clay, a 0.3-inch ball of green modeling clay and a 0.3-inch ball of blue modeling clay.
Make an index card for each planet and dwarf planet by writing its name on top. Stick one pin into the card for Mercury, and the other pin into the card for Mars, with the pinheads sticking out to represent the size of these planets. Glue one peppercorn to the card for Venus, and the other peppercorn to the card for Earth. Glue the red ball to the card for Jupiter, the yellow ball to the card for Saturn, the green ball to the card for Uranus and the blue ball to the card for Neptune. Last, glue a grain of sand to the card for Pluto. Allow the glue to dry before proceeding.
Place the 8-inch foam ball at one end of a table to represent the sun. Arrange the planet and dwarf planet cards on the table in the correct order, based on their increasing distance from the sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. Explain that on this scale, 1 inch represents 100,000 miles. Earth is about 8,000 miles in diameter, while the sun is about 800,000 miles in diameter. Thus, they’re represented by a .08-inch peppercorn and an 8-inch foam ball, respectively.
Take the foam ball and the cards outside. Place the foam ball at a predetermined point, making sure that you have about half a mile of open space on one side of it in which you can spread out the planets, plus Pluto. Explain that because 1 inch represents 100,000 miles, 1 yard represents 3,600,000 miles. The distance between the sun and Mercury is about 36,000,000 miles. Therefore, Mercury should be 10 yards from the foam ball. Measure out this distance — preferably by using a GPS-equipped pedometer — and place Mercury’s card on the ground.
Walk nine more yards in the same direction to place Venus, which is about 67,000,000 miles from the sun. Walk another seven yards to place Earth. At this point, look back at the 8-inch foam ball and note that from here, it appears approximately the same size as the sun seems to be when viewed from Earth.
Walk 14 yards to place the card for Mars. Walk 95 additional yards to place the card for Jupiter.
Place Saturn 112 yards from Jupiter. Place Uranus 249 yards from Saturn. Note that Uranus marks the approximate halfway point between the sun and Pluto.
Place Neptune 281 yards from Uranus. Place Pluto 242 yards from Neptune. Having put the last card in position, you have traveled about 1,019 yards. At this scale, that represents more than 3.6 billion miles. It takes the light from the sun 5.5 hours to travel this distance.