If the Sun Were the Size of a Balance Ball, How Big Would Earth Be?
I’m Ken Kuwako, your Science Trainer. Every day is an experiment.
Here’s a question for you. If you shrank the Sun down to a 50 cm diameter balance ball, how big do you think Earth would be? A soccer ball? A ping-pong ball? …Believe it or not, the answer is just 1 mm. It would be so tiny that you’d have to squint to see it! Today, let’s take a journey into the wonderfully surprising world of a “scale model of the Solar System.”
While flipping through a science reference book, I came across an intriguing idea: “What if the Sun were a sphere 50 cm in diameter? What would happen to the other planets?” I immediately decided to make a calculation sheet to find out. For the model Sun, I used a 50 cm diameter balance ball. You can find the spreadsheet here.
The Planets Turn Into Familiar Objects
Once I ran the numbers, I discovered that the other planets could be represented by surprisingly familiar objects when the Sun is scaled down to a 50 cm balance ball.
Bead 8 mm in diameter
Ping-pong ball 44 mm in diameter
Soccer ball 220 mm in diameter
Baseball 70 mm in diameter
Beach ball 260 mm in diameter
Balance ball 500 mm in diameter
I also prepared separate sheets for the questions and answers, with the calculation formulas already entered in the answer sheet. Here are the results.
And what about Earth? Its diameter would be a mere 1 mm. “Wait, that tiny?” You’re probably not the only one who finds that surprising. Compared with the size of the Sun, even Jupiter would be no bigger than a ping-pong ball. Suddenly, the enormous scale of the universe becomes something you can almost hold in the palm of your hand.
Let’s Scale the Distances to the Planets, Too
Now that we have our balance ball (the Sun) sitting right in front of us, where would the other planets be orbiting? I ran the numbers for that, too. Here’s what I got.
A handy way to visualize these distances is a web service that lets you “draw circles on Google Maps.” Even Mercury, the closest planet to the Sun, would be 21 meters away from our model Sun (the balance ball). That’s already far enough to take you outside the room! Try using the app to draw the circles around your home or school, and you’ll discover some surprisingly interesting things.
It would look something like this. The Sun sits at the center, with Mercury, Venus, Earth, and the other planets spreading outward.
Overlaying the model on a real map really drives home just how enormous the Solar System is. I’ve also added another version to the spreadsheet where the Sun’s diameter is scaled up to 1 meter (100 cm), so give that one a try, too.
If Earth Were a 100 cm Sphere, What Would Happen to Tokyo?
Apparently, the idea of “What would Earth look like if it were a 100 cm sphere?” has already been turned into a book. And the details are absolutely mind-blowing.
The Moon would be about the size of a beach ball, orbiting roughly 30 meters from Earth. The Sun would be 12 km away and, astonishingly, would be about the size of Tokyo Dome. From the perspective of a 100 cm Earth, the Sun would shine as brightly as 14 billion 100-watt light bulbs switched on at once. It’s an incredible reminder of just how enormous the Sun really is.
Now, if we map these positions onto the JR Tokaido Line, the Solar System looks like this.
・Earth would be around Omori Station in Tokyo, with a diameter of 100 cm.
・Mercury would be around Shinagawa Station, with a diameter of 40 cm.
・Venus would be around Oimachi, with a diameter of 95 cm.
・Mars would be around Kawasaki Station, with a diameter of 50 cm.
・Jupiter would be around Hiratsuka Station, with a diameter of 11 m.
・Saturn would be around Mount Fuji, with a diameter of 9 m.
I wanted to see whether these numbers really checked out, so I did the calculations myself.
The numbers are slightly different from those in the reference I mentioned earlier, but they’re broadly consistent. According to my calculations, the Sun would be about 100 meters in diameter. “A 100-meter sphere” may still be difficult to picture, but I looked it up and discovered that the giant Ferris wheel that once stood at Palette Town in Odaiba was exactly 100 meters in diameter.
Once you imagine that giant Ferris wheel as the “Sun,” the sheer scale of our Solar System becomes truly astonishing.
Turn It Into a Display and Experience It Together
Based on these calculations, I also created a display poster (Google Slides). If you find it useful, please feel free to use it for your classes, science projects, or other activities.
Later on, I decided to give the display an upgrade. Take a look at this version, too!
These are 45 mm diameter polystyrene balls I bought at Seria, a Japanese 100-yen shop.
I attached one of them to the display at the “ping-pong ball” position using a hot glue gun.
These are beads I also bought at Seria. They are just 4 mm in diameter.
I attached these to the display as well.
Compared with simply looking at a flat diagram or graph, turning the model into something three-dimensional that students can actually see and touch makes the enormous scale of the Solar System much more engaging—and much easier to appreciate.
Questions, Requests, and More
Let’s bring the wonders and excitement of science a little closer to home! I share fun science experiments you can try at home, along with simple tips and explanations to help you get the most out of them. Feel free to explore the site and see what you can discover!
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