Rocket spreads paper, a ruler and scissors across the Sky Deck table. "One centimeter for Earth. Everything else follows."
He cuts a circle 1 centimeter across and holds it up. "Tiny. Now Jupiter." He draws a circle 11 centimeters across.
Raven measures a loop of string on the floor, 110 centimeters across. "What do you notice? That is the Sun."
Rocket sets his little Earth inside the string circle. It almost disappears.
"Mercury is less than half a centimeter," Raven says. "I can barely cut it."
Nova hovers over the floor circle. "Last week the model hid the sizes," she says. "This week it hides the distances. Notice what each model gives up."
Today you cut paper circles for all eight planets at one scale: Earth is 1 centimeter across.
Each diameter from the NASA fact sheet was divided by Earth's diameter, 12,756 kilometers, to get the size in centimeters.
The Sun at this scale is about 110 centimeters across, too big for paper. You lay it out in string on the floor.
| World | Diameter (km) | Paper size (cm) | Something about that size |
|---|---|---|---|
| Mercury | 4879 | 0.4 | a tiny bead |
| Venus | 12,104 | 0.9 | a small bead |
| Earth | 12,756 | 1.0 | a small bead |
| Mars | 6792 | 0.5 | half a bead |
| Jupiter | 142,984 | 11.2 | a small plate |
| Saturn | 120,536 | 9.4 | a saucer |
| Uranus | 51,118 | 4.0 | a bottle cap |
| Neptune | 49,528 | 3.9 | a bottle cap |
| The Sun | about 1,400,000 | about 110 | a string circle on the floor |
| Observation | What I found |
|---|---|
| How many Earth circles fit across Jupiter | |
| How much of the Sun circle the eight planets fill | |
| Planets hard to see from standing height | |
| Something in my home about the size of paper Jupiter |
Right: the sizes. Every planet is in true proportion to the others and to the Sun.
Right: the two families. The four tiny circles and the four big ones sort themselves on the table.
Wrong: the distances. At this scale Earth would sit about 117 meters from the string Sun, far outside the room.
OpenStax Astronomy makes the same point. A model that shows sizes well cannot also show distances in one room.
| Model claim | True or false? |
|---|---|
| At this scale Earth is 1 centimeter across. | ? |
| Paper Jupiter is about 11 times wider than paper Earth. | ? |
| The paper model shows the planets' true distances from the Sun. | ? |
| The Sun circle is about 110 times wider than paper Earth. | ? |
Careful cutting. Tomorrow you read the rest of the NASA fact sheet: days, years, gravity, heat, moons and rings.