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2021, June 16, Sidewalk Solar System

Jupiter and its largest moons.

This "family portrait," a composite of the Jovian system, includes the edge of Jupiter with its Great Red Spot, and Jupiter's four largest moons, known as the Galilean satellites. From top to bottom, the moons shown are Io, Europa, Ganymede and Callisto. The Great Red Spot, a storm in Jupiter's atmosphere, is at least 400 years old. (NASA Photo)


June 16, 2021:  A summer project is to build a sidewalk solar system model. The scale uses the sun’s size as the size of a basketball.  Earth’s distance is 88 feet.

Photo Caption – A solar system model with the sun the size of a basketball.

by Jeffrey L. Hunt

Build a sidewalk solar system model. It’s a great summer project to show children the relative sizes and distances of the sun and planets.

The equipment needed is a tape measure (the longer, the better), sidewalk chalk for temporary markers or spray paint for a longer-term model.

With any model, making all the scales work is the challenge.  This is evident with the relative sizes and distances of the planets. Can we make the planets large enough, but keep their distance from the sun reasonable?  Well, not really.  A long neighborhood sidewalk is needed.

We start with the sun’s actual diameter, 840,000 miles.  Let’s reduce it to the diameter of a basketball, about 9.55 inches. At this scale the planets’ sizes are tiny, especially the inner planets until Jupiter is marked.  Then place the planets at their distances from the sun.

ObjectScale size (inches)Scale Distance (feet)

If you’re building a classic solar system, including Pluto, its distance from the sun in 2021 is 3018.4 feet from the sun.  The planet is small, only 1/200 inch, just a tiny dot.

Have fun with this model.

Articles and Summaries

2021, October 5: Skinny Moon, Evening Planet Pack

October 5, 2021: Before sunrise, a very thin moon is visible in the eastern sky.  The evening planet pack – Evening Star Venus, Jupiter, and Saturn – are visible at the same time after sundown.

2021, October 3:  Lunar Slice, Evening Planet Pack

October 3, 2021:  Before sunrise, the thin crescent moon is in the eastern sky, to the lower left of Regulus.  After sunset, the planet pack – Evening Star Venus, Jupiter, and Saturn – shine brightly.

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