What it shows
The planets are not evenly spaced. On a scale where the Sun to Neptune is 100 sheets of toilet paper, the four rocky planets all fit inside the first 5 sheets and the gaps between the outer planets grow huge, something no picture in a textbook can show.
The science
The astronomical unit (AU) is the average Earth to Sun distance, about 150 million kilometres. Neptune orbits at about 30 AU, so dividing 100 sheets by 30 gives 3.33 sheets per AU. Multiplying each planet's distance in AU by that number gives its position on the roll. Models in books squeeze the distances because, at a scale where the planets are visible as dots, the roll would need to be hundreds of metres long.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A roll of toilet paper with at least 100 sheets
- A marker
- A long corridor or a playground
- A table of planet distances in astronomical units
- Small paper planet labels
- Tape
Safety
This project uses safe, everyday materials. Still, read the rules below with a parent before you start.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Write the distances: Mercury 0.4 AU, Venus 0.7, Earth 1, Mars 1.5, Jupiter 5.2, Saturn 9.5, Uranus 19.2, Neptune 30.
Multiply each by 3.33 to get the sheet number and round to one decimal.
Unroll the paper down the corridor and tape the first edge down as the Sun.
Count sheets and mark each planet at its sheet number with the marker.
Tape a label on each mark and draw the planet as a dot.
Walk the length and note how crowded the first five sheets are compared with the last fifty.
Measure the roll in metres and work out how many kilometres one sheet represents.
Photograph or sketch the layout and present the scale in a table.
What you should see
A 100-sheet strip with Mercury at sheet 1.3, Earth at 3.3, Mars at 5, Jupiter at 17, Saturn at 32, Uranus at 64 and Neptune at 100, showing the huge empty outer solar system.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is an astronomical unit?
The average distance from the Earth to the Sun, about 150 million kilometres.
2Why can a book not show distances and sizes to the same scale?
At a scale where the planets are visible, the model would be hundreds of metres long.
3Which planet is about 5 AU from the Sun?
Jupiter.
4How long does sunlight take to reach Neptune?
About 4 hours, compared with 8 minutes for the Earth.
Take it further
Work out where the nearest star, about 270,000 AU away, would be on the same scale.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
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