“The Thousand-Yard Model, or The Earth as a Peppercorn” — © 1989 Guy Ottewell, published by Universal Workshop. Reproduced here with attribution, following the same practice used by educational and outreach organisations worldwide — including NOIRLab and the Rainforest Information Centre, where John Seed has used it for many years as part of the Deep Ecology workshops. Guy Ottewell has continued to write and publish astronomical guides through Universal Workshop — his shop is worth a visit if this exercise is useful to you.

This is the Home Page for visualizing just how BIG our Solar System really is. In accordance with the booklet by Guy Ottewell, here is an outdoor activity designed to illustrate the vast scale factor of our Solar System using a mere peppercorn to represent the size of the Earth.

Can you picture the dimensions of the solar system? Probably not, for they are of an order so amazing that it is difficult either to realize or to show them.

The fact is that the planets are mighty small and the distances between them are almost ridiculously large. To make any representation whose scale is true for the planets’ sizes and distances, we must go outdoors.

The following exercise could be called a Model, a Walk or a Happening. Since it is simple, it may seem suitable for children only. It can, indeed, be done with children down to the age of seven. Yet it can also be done with a class consisting of professors of astronomy. It will not waste their time. They will discover that what they thought they knew, they now apprehend. To take another extreme, the most uncontrollable high-school students or the most blasé college students unfailingly switch on their full attention after the first few paces of the excursion. There is one other party that may profitably take the planet-walk, and that is yourself, alone. Reading the following description is no substitute: you must go out and take the steps and look at the distances, if the awe is to set in.

Gathering the objects

First, collect the objects you need. They are:

You may suspect it is easier to search out pebbles of the right sizes. But the advantage of distinct objects such as peanuts is that their rough sizes are remembered along with them. It does not matter if the peanut is not exactly 0.3 inch long, nor that it is not spherical.

A standard bowling ball happens to be just 8 inches wide, and makes a nice massive Sun — but it may not be easy to find and certainly isn’t easy to carry around. There are plenty of inflatable balls which are near enough in size.

The three pins must be stuck through pieces of card, otherwise their heads will be virtually invisible. If you like, you can fasten the other planets onto labelled cards too.

Begin by spilling the objects out on a table and setting them in a row. Here is the moment to remind everyone of the number of planets — nine, in Ottewell’s original count — and their order: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.

The first astonishment is the contrast between the great round looming Sun and the tiny planets. (And note a proof of the difference between reading and seeing: if it were not for the picture, figures such as “8 inches” and “0.08 inch” would create little impression.) Look at the second peppercorn — our “huge” Earth — up beside the truly huge curve of the Sun.

Establishing a distance scale

Having set out the objects with which the model is to be made, the next thing is to ask: “How much space do we need to make it?” Children may think the table-top will suffice, or perhaps the room, or the corridor outside. To arrive at the answer, we have to introduce scale.

This peppercorn is the Earth we live on. The Earth is eight thousand miles wide. The peppercorn is eight hundredths of an inch wide. What about the Sun? It is eight hundred thousand miles wide, and the ball representing it is eight inches wide. So one inch in the model represents a hundred thousand miles in reality.

This means that one yard (36 inches) represents 3,600,000 miles. Take a pace: this distance across the floor is an enormous space-journey called “three million six hundred thousand miles.” Now, what is the distance between the Earth and the Sun? It is 93 million miles. In the model, this will be 26 yards. This still may not mean much until you get one of the class to start at the side of the room and take 26 paces — they come up against the opposite wall at about 15!

Clearly, it will be necessary to go outside.

Take a hike

Hand the Sun and the planets to members of the group, making sure each person knows the name of the object they are carrying, so as to be able to produce it when called upon.

You will have found in advance a spot from which you can walk a thousand yards in something like a straight line. This may not be easy — straightness of the course is not essential, nor do you have to be able to see one end from the other. You may have to “fold” it back on itself. It should be a walk that will make a good story afterwards, like “all the way from the flagpole to the garden gate!”

Put the Sun ball down, and march away as follows. (After the first few planets, you will want to appoint someone else to do the actual pacing — call this person the “Spacecraft” — so that you are free to talk.)

Already the thing seems beyond belief. Mercury is supposed to be so close to the Sun that it is merely a scorched rock, and we never see it except in the Sun’s glare at dawn or dusk — yet here it is, utterly lost in space! As for the Earth, who can believe that the Sun could warm us if we are that far from it?

The correctness of the scale can be proved to sceptics (of a certain maturity) on the spot. The apparent size of the Sun ball, 26 paces away, is now the same as that of the real Sun — half a degree of arc, or half the width of your little finger held at arm’s length. (If both the size of an object and its distance have been scaled down by the same factor, then the angle it subtends must remain the same.)

Now come the gasps, at the first substantially larger leap:

From now on, amazement itself cannot keep pace, as the intervals grow extravagantly:

You have marched more than half a mile! (The distance in the model adds up to 1,019 paces. A mile is 1,760 yards.)

To look back toward the Sun ball — no longer visible even with binoculars — and to look down at the pinhead Pluto, is to feel the terrifying wonder of space.

Afterwards

That is the outline of the Thousand-Yard Model. But be warned that if you do it once, you may be asked to do it again. Children are fascinated by it enough to recount it to other children; they write “stories” which get printed in the school paper; teachers from other schools call and ask you to demonstrate it.

The outline can bear variation and elaboration. There are different things you can remark on during the pacings from one planet to the next, and there are extra pieces of information that can easily be grafted on — these lead forward, in fact, to the wider reaches of the universe, and make the planet-walk a convenient introduction to a course in astronomy (or to the Cosmic Walk that follows it in our own Deep Ecology practice). But omit them if dealing with children young enough to be confused, or if you yourself would prefer to avoid mental vertigo.

It’s recommended to stop reading at this point, carry out the walk once, and reflect on it before elaborating further.