You will need

• a willing adult with a car
• a backpack full of planets:
  • a whole peppercorn
  • 2 marbles
  • a pea
  • a grain of sand
  • a cantaloupe
  • a softball
  • 2 apples (small McIntosh are good)
• a straight pin
• a bicycle
• a fairly straight road or street 31/2 miles long

What to Do

Find a street in your town that follows as straight a line as possible for 31/2 miles. Your starting point for your Solar System tour is the Sun, which at this scale would be 4 feet across - about the size of the front end of a car. Choose a parked car as your Sun. The table below shows you which items in your backpack are which planets, and how far away they should be from your starting point. Ask an adult friend with a car to help you measure the distances and identify landmarks along the street at each distance. Now you're ready for your tour.

Hop on your bike at the "sun" carrying the planets in your pack. As you pass the 100 yard landmark, get out the peppercorn Mercury and place it on the ground. Look back at the Sun. Can you see it? This is how big the real Sun would look if you were standing on the real Mercury. Continue on through the rest of the Solar System, placing the planets in their orbits as you pedal along. On your way back from Pluto, be sure to pick up all the planets!

Planet	Model Diameter	Model Distance (from Sun)
Sun	giant 4 foot beachball (or front end of a parked car)	- - -
Mercury	peppercorn	100 yards
Venus	marble	200 yards
Earth	marble	250 yards
Mars	pea	350 yards
Ceres(largest asteroid)	grain of sand	1/4 mile
Jupiter	cantaloupe	1/2 mile
Saturn	softball	1 mile
Uranus	apple	2 miles
Neptune	apple	3 miles
Pluto	pin head	3 1/2 miles

Each yard you travel in this activity is equal to 360,000 miles. Bet you've never pedaled that fast before! In fact, you'll be racing through space at a speed that would be physically impossible in the real Solar System, because it would be faster than the speed of light. Light's speed, 186,000 miles per second, would be represented in your model Solar System by a very slow stroll of 1 step per second.

As you pedal along, you'll start to really appreciate the vast distances of space. And think of it -- the Solar System is just a tiny corner of the universe. How far would the nearest star (besides the Sun), Alpha Centauri, be at the scale of this model? You would have to bicycle around the entire circumference of the Earth to get there!

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