Skip to content

A model solar system

Space and time · level 2, lesson 6 of 6

A question to start

Books often draw the planets as big balls, close together round the Sun. What would a model look like if everything were the right size and the right distance apart?

The idea

Shrink everything by the same amount: say, 10 billion times. Then the Sun becomes a ball about 14 cm across, the size of a grapefruit. Everything else shrinks too:

Object Size in the model Distance from the Sun
Sun a grapefruit, 14 cm in the middle
Earth a pinhead, 1.3 mm 15 m
Moon a speck, 0.35 mm 4 cm from the Earth
Mars a grain of sand, 0.7 mm 23 m
Jupiter a grape, 14 mm 78 m
Neptune a pea, 5 mm 452 m

The Earth is a pinhead 15 big steps from the grapefruit. Mars is a grain of sand 23 m away. Neptune is nearly half a kilometre off. Space is mostly empty.

Sun: 14 cmEarth, 15 mMars, 23 mJupiter, 78 m

The distances along the path are to scale; the balls are drawn bigger so you can see them.

Worked examples

1. Shrinking the Sun. The Sun is 1,392,000 km across. Shrunk 10 billion times: 139 mm, about 14 cm.

2. Shrinking the distance. The Earth is 150 million km from the Sun. Shrunk 10 billion times: 15 m.

3. Mars. 228 million km shrinks to about 23 m. Mars is a tiny grain only 8 m beyond the Earth's pinhead.

Try it

  1. In the model, how big is the Sun?
  2. How far from the Sun is the Earth in the model?
  3. Which is farther in the model: Mars at 23 m or Jupiter at 78 m?
  4. What does the model show about space?
Answers
  1. About 14 cm, like a grapefruit.
  2. About 15 m.
  3. Jupiter.
  4. That it is mostly empty: tiny planets with huge gaps between them.

Common mistake

"Pictures in books are to scale." To fit on a page, books draw the planets far too big and far too close. Real space is mostly empty.

Where it leads