Build Your Own Solar System: The Ultimate STEM Project for Middle School

Our Solar System has 8 planets, countless moons, and distances that stretch beyond imagination. In this project, middle school students (ages 12–15) build an impressive three-dimensional model using polystyrene foam balls and acrylic paints — while learning about the relative sizes, distances, and characteristics of each planet. Perfect for a Science or Astronomy class, or as a showstopper at your next school fair!

What You'll Need

From Our e-shop

  • Polystyrene foam balls in multiple sizes (Ø 4, 5, 6, 8, 10 and 12 cm) — Find them here
  • Acrylic paints — a set of 12 colours works perfectly
  • Fine-tip brushes for detail work
  • Metal floral wire sticks for mounting the planets
  • Glitter or gold powder for the Sun

Items You Probably Have at Home

  • Large black cardboard (A2) for the base
  • String or thick thread
  • Scissors and a hot glue gun
  • White marker for labels
  • Ruler and pencil for drawing orbits

Which Ball for Which Planet?

Follow this guide for the correct size and colour for each planet:

  • Mercury: Ø 4 cm — grey
  • Venus: Ø 6 cm — yellow-orange
  • Earth: Ø 6 cm — blue with green continents
  • Mars: Ø 5 cm — red-brown
  • Jupiter: Ø 12 cm — beige with brown horizontal bands
  • Saturn: Ø 10 cm — golden-yellow with a cardboard ring
  • Uranus: Ø 8 cm — pale blue-green
  • Neptune: Ø 8 cm — deep blue

Tip: Stick each ball onto a toothpick before painting — it keeps your fingers clean and gives you full control!

 

Step-by-Step Instructions

Step 1: Plan Your Scale and Orbits

Before you start painting, lightly sketch the elliptical orbits of the planets on your black cardboard using a pencil and ruler. Keep in mind that real distances in space are enormous — if Earth were the size of a marble, the Sun would be about 15 metres away! For this model, we use a simplified scale so everything fits on the board.

Step 2: Paint the Foam Balls

Use your acrylic paints following the colour guide above. If the paint doesn't grip the foam easily, apply a thin coat of white primer first. For Saturn, cut a ring out of cardboard, paint it separately and glue it on once everything is dry. Acrylics dry fast, so you can apply a second coat within minutes.

Step 3: Create the Sun

Use the largest ball (12 cm or bigger) for the Sun. Paint it bright yellow-orange and add glitter or gold powder to give it a glowing effect. Once dry, fix it firmly to the centre of your base with hot glue.

Step 4: Mount the Planets

Push a metal wire stick through each ball. You can either glue each planet directly onto the cardboard along its orbit, or hang them with string to create a stunning mobile that can be suspended from the ceiling.

Step 5: Add Labels and Present

Use a white marker to write the name of each planet along with 1–2 key facts: distance from the Sun in AU, number of moons, surface temperature. Each group then presents "their" planet to the class!

 

What Students Learn

  • Relative sizes and distances of planets — understanding scale in space
  • Differences between inner (rocky) and outer (gas giant) planets
  • Links to Physics: gravity, orbital motion, astronomical units (AU)
  • Teamwork and presentation skills

Quick Materials Summary

  • Base: Black A2 cardboard
  • Planets: Polystyrene foam balls in various sizes
  • Colours: Acrylic paints and fine brushes
  • Mounting: Metal wire sticks or string for a hanging mobile

Visit our e-shop to find polystyrene balls, acrylic paints, brushes and everything else you need for this and many more STEM projects. Happy making!