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. The first astonishment is the contrast between the great round looming Sun and the tiny planets. 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 scale. This peppercorn is the Earth we live on. The peppercorn is eight hundredths of an inch wide. It is eight hundred thousand miles wide. The ball representing it is eight inches wide.