Curiosity · The scale of the universe

The scale of space

If the Earth were a chickpea, how far away would the Moon be? The nearest star? Our galaxy? Use scale models to turn the mind-boggling distances of the universe into everyday objects, and find out why space is mostly empty.

17 min
2 simulations
Mini quiz

Updated: 16 October 2026

Preview

The question

In textbook pictures, the Moon sits right next to the Earth like a small ball. In reality, how many Earths would fit between the Earth and the Moon? And how far would you have to travel to reach the star nearest the Sun? The human brain struggles to feel numbers this big. In this lesson we'll make them something you can get hold of.

Try it yourself

No account needed: change the values and check your answer. Some simulations ask for a prediction before they start; it doesn't matter whether it's right or wrong.

Number line

Chickpea Earth, peppercorn Moon

Drag the marker or move it with the arrow keys, then press Check.

Predict first

If the Earth were a chickpea, how far from it do you think the Moon would be?

It doesn’t matter whether you’re right; the simulation opens once you choose.

Ordering

The universe from near to far

Drag the cards by their handles, or move them up and down with the arrows.

Predict first

Which of these could be true about the distance of Neptune, at the edge of our Solar System, compared with the nearest star?

It doesn’t matter whether you’re right; the simulation opens once you choose.

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Frequently asked

5 questions

Is the Moon as close to Earth as textbook pictures show?

No. The Earth–Moon distance averages 384,400 km; about 30 Earths would fit in between. If Earth were a 1 cm chickpea, the Moon would be a 3 mm dot about 30 cm away.

Why aren't space pictures in books drawn to scale?

If they were drawn to scale, either the planets would be too small to see or the Moon would fall off the page. These pictures are meant to show the objects, not the distances.

Are stars scattered in between the planets?

No. The nearest star to the Sun, Proxima Centauri, is about 40 trillion km away, roughly 9,000 times as far as Neptune. If the Sun were a 1 m ball, that star would be about 29,000 km away.

What is an astronomical unit?

It is the distance between Earth and the Sun, about 150 million km, written AU for short. It is used for distances in the Solar System: for example, Neptune is about 30 AU, or 4.5 billion km, from the Sun.

Why do scientists write distances using powers of ten?

Distances in space grow so fast that counting zeros becomes hard. With powers of ten, raising the exponent by one makes the distance 10 times bigger: Earth–Moon is about 4 × 10 to the power 5 km, and the nearest star about 4 × 10 to the power 13 km.