Tuesday

Raven lays the NASA fact sheet on the hallway floor. "Neptune: 4,515 million kilometers. Mercury: 57.9 million."

"Our hall is nine meters," Rocket says. "So Neptune at nine meters. Then I just shrink everything the same amount."

"What do you notice about the inner planets?" Raven asks. "Mercury would be twelve centimeters from the Sun. Earth thirty."

Nova projects a line of glowing dots down the hall. "The first four crowd together," she says. "The giants spread out."

Rocket tries Earth's size at that scale and frowns. "Earth would be smaller than a grain of sand."

"One scale cannot do both," Raven says. Nova hums. "Now you know the trade-off. Choose."

NASA's Planetary Fact Sheet lists each planet's average distance from the Sun in millions of kilometers, and its diameter in kilometers.

NASA says our solar system has eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Pluto is a dwarf planet.

The first four are terrestrial planets with solid surfaces. The giant planets have swirling gases above a core. Jupiter and Saturn are gas giants, Uranus and Neptune ice giants.

A scale is a rule: so many real kilometers for each centimeter of model. The last column uses 1 centimeter for every 5 million kilometers.

To find a model distance, divide the real distance in millions of kilometers by 5. Neptune: 4,515 divided by 5 is 903 centimeters, about 9 meters.

If your space is shorter, pick a bigger number of kilometers per centimeter. Divide every planet by the same number so the scale stays true.

OpenStax Astronomy describes a model that shrinks everything by one billion. Earth becomes a 1.3 centimeter ball and sits 150 meters from a Sun 1.5 meters across.

At the hallway scale, Earth's 12,756 kilometers shrink to about three hundredths of a millimeter. That is the scientific limit from Monday.

Your plan has numbers now. Tomorrow is Sky Deck Lab: build it, then test it with a tape measure.