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 represen-
tation 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 profes-
sors of astronomy. It will not waste their time. They will dis-
cover that what they thought they knew, they now apprehend. To
take another extreme, the most uncontrollable high-school stu-
dents or the most blase 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 descrip-
tion is no substitute: you must go out and take the steps and
look at the distances, if the awe is to set in.
First, collect the objects you need. They are:
ball, diameter 8.00 inches
pinhead, diameter 0.03 inch
peppercorn, diameter 0.08 inch
chestnut or a pecan, diameter 0.90 inch
a hazelnut or an acorn, diameter 0.70 inch
a peanut or coffeebean, diameter 0.30 inch
second peanut or coffeebean
Pluto <http://www.seds.org/nineplanets/nineplanets/pluto.html>- a
third pinhead (or smaller, since Pluto is the smallest planet)
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 .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, so I couldn't resist putting it in the
picture. 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 labeled 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 -9- and their order--MVEMJSUNP. (This mvemonic could be
made slightly more pronounceable by inserting the asteroids in
their place between Mars and Jupiter: MVEMAJSUNP.)
The first astonishment is the contrast between the great round
looming Sun and the tiny planets. (And note a proof of the dif-
ference between reading and seeing: if it were not for the pic-
ture, the figures such as "8 inches" and ".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 that the table-top will suffice, or a fraction
of it, or merely moving the objects apart a little. Adults think
in terms of the room or a fraction of the room, or perhaps the
corridor outside. To arrive at the answer, we have to introduce
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. 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 till you get one of the class to
start at the side of the room and take 26 paces. He comes up
against the opposite wall at about 15!
Clearly, it will be necessary to go outside.
Hand the Sun and the planets to members of the class
<Handing.html>, making sure that each knows the name of the
object he or she is carrying, so as to be able to produce it when
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 of it from the other. You may have
to "fold" it back on itself. It should be a unit that will make a
good story afterwards like "All the way from the flagpole to the
Take a Hike!
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" or "Pace-
craft"-so that you are free to talk.)
10 paces. Call out "Mercury, where are you?" and have the Mer-
cury-bearer put down his card and pinhead, weighting them with a
pebble if necessary.
Another 9 paces. Venus puts down her peppercorn.
Another 7 paces. Earth
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 skeptics (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 or 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.)
Another 14 paces. Mars
Now come the gasps, at the first substantially larger leap:
Another 95 paces to Jupiter
Here is the "giant planet"-but it is a chestnut, more than a city
block from its nearest neighbor in space!
From now on, amazement itself cannot keep pace, as the intervals
Another 112 paces. Saturn
Another 249 paces. Uranus
Another 281 paces. Neptune
Another 242 paces. Pluto
You have marched more than half a mile!
(The distance in the model adds up to 1,019 paces. A mile is
To do this, to look back toward the Sun ball, which is no longer
visible even with binoculars, and to look down at the pinhead
Pluto, is to feel the terrifying wonder of space.
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 you up and ask you to demonstrate it.
So 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. But omit them
if you are dealing with children young enough to be confused, or
if you yourself would prefer to avoid mental vertigo.
I recommend that you stop reading at this point, carry out the
walk once, and then read the further notes.