Explore Worlds
Find Life
Defend Earth
Hands-on activity: Sidewalk chalk
The mission
Walk your neighborhood to make your own scale model of the Solar System, then draw how comets crash down to Earth.
Age range: 4-8
What you’ll need:
- Sidewalk chalk
- A smartphone/stopwatch
- Somewhere paved to go on a walk
NGSS compatibility (for U.S. teachers):
Disciplinary Core Ideas: 1-ESS1-1, 1-ESS1-2, 5-ESS1-1, and 5-ESS1-2.
Science & Engineering Practices: developing and using models; constructing explanations; using mathematics.
Crosscutting Concepts: patterns; systems and system models; scale, proportion, and quantity.
Background
When a child starts to learn how mind-bogglingly big the Universe is, they take one of their first steps into a broader sense of wonder and cosmic perspective. It’s emotional but also profoundly practical: we’re just answering the question, “Where are we?” Once kids understand where Earth is compared to the Sun and how the Solar System is arranged, they can go on to learn about their place in the wider galaxy or the entire observable Universe. By having kids get outside and feel the distance under them, this activity makes the lesson about as visceral as it can get. As a bonus, the chalk in this activity doubles as a tool for kids to discover how comets and asteroids break up as they fall through our atmosphere.
Note: This activity involves walking a short distance, about six minutes at a grade schooler’s pace or quarter-mile (though you can also choose to walk for longer). A paved location where you can walk safely for that distance or more, like a park or school, is ideal. Your own neighborhood might work great, too.
1
On a sidewalk or pavement where it’s safe to walk, pick the starting point for your Solar System. Draw the Sun here.
- To keep the scale right, your Sun should be about three times bigger than a hula hoop (about 10 feet), or a little smaller than a sedan.
2
To get to Mercury, walk at a normal pace for 100 seconds, then stop.
- You can also time it by counting, “1 banana, 2 banana…” all the way to 100, but that might get tiring after enough bananas.
- Draw Mercury, the smallest planet. It should only be a quarter-inch wide, about as big as the grooves in the sidewalk.
3
Continue on for 80 seconds. Here, draw Venus — it should be about the size of a bottle cap.
🪐 Are the planets always in this order?
Not exactly. The planets almost never happen to line up in a straight row out from the Sun. Earth might be on one side of the Sun while Venus is somewhere on the other side, for example. But Earth is always farther away from the Sun than Venus, and Venus is always farther away from the Sun than Mercury.
What about from Earth’s perspective? The planet closest to Earth changes over time. When Venus and Earth are both on the same side of the Sun, then Venus would be the closest planet to Earth. But if Venus and Mars were on the opposite side of the Sun while Mercury was on the same side as Earth, then Mercury would be closest to Earth.
5
After Earth, Mars is only two minutes away. It should be about half as big as you drew Earth.
6
Jupiter is much farther: a full sixteen minutes.
- If you get to Jupiter, draw it the size of a normal piece of paper or a birthday cake (about a foot wide).
7
You’d have to walk another 20 minutes past Jupiter to reach Saturn. It would be a little smaller than Jupiter, about the size of a dinner plate.
☄️ Why don’t we keep going to Pluto?
Just getting to Uranus — the next planet after Saturn — would mean walking another 40 minutes. Neptune is still 2 hours and 40 minutes of walk away, and Pluto is at least that far, if not farther (Pluto’s distance from the Sun changes a lot over time). To get to the next nearest star after the Sun, Proxima Centauri, you’d have to keep walking for two years straight.
8
Wherever you’ve ended up, draw your comet.
- Compared to planets, the comet would be too small to be visible if we kept it on the same scale. So don’t worry about sizes for this part — make the comet as big as you want.
- Make sure the comet’s tail points away from your Sun.
- Explanation: A comet's tail rarely “trails” it like a flag. The tail is being blasted away by the Sun’s radiation, so it doesn’t depend on the direction the comet is moving in — instead, the tail will tend to point away from the Sun.
9
Walk back to Earth. Draw your comet heading toward Earth along the way.
- Comets originate in the outer Solar System, typically past Jupiter and Saturn. There, it’s cold enough for their ice to stay frozen — but as the comet comes closer to the Sun, the ice turns to gas and falls away from the comet, making a tail.
10
Draw your comet getting smaller as it gets closer to the ground. By the time it hits the ground, it should only be 1/20th the size of the comet you drew, somewhere out past Earth.
- Explanation: As comets and asteroids fall through our atmosphere, they rub or push against the air and heat up, glowing as shooting stars. They shed and fall apart until they’re either a fraction of their original size or completely destroyed. On average, the remains of comets and asteroids on Earth, called meteorites, are less than 1/20th their size when they entered our atmosphere.
- To see shooting stars for yourself, check out our guide to the next meteor shower!