Tabletop Solar System Orrery

You will need

• Cardboard for the baseA shoebox lid or two layers of cardboard taped together; clean, wiped down; recycle when done

  Use cardboard from food or household goods boxes only, not from chemical packaging; wipe surfaces before use.

• Cardboard tubeOne paper towel tube, for the central mast
• Coat hanger wire or pipe cleanersFor the orbital arms; adult bends wire ends; pipe cleaners are safer for child to shape

  If using coat hanger wire, an adult should bend all sharp ends into closed loops before the child handles any piece.

• String or thin yarnAbout 6 feet total; cut into eight graduated lengths for hanging planets
• Newspaper or scrap paperCrumpled into eight balls of different sizes, for the planets
• Packing tape or masking tapeTo hold the mast, arms, and planet strings in place
• RulerFor measuring arm lengths and string lengths
• Washable markersFor coloring and labeling each planet ball
• Reference sheet of planet order and sizesHand-drawn or printed; any size; kept beside the build as a working reference
• Watercolor paints and a small brushoptionalFor painting planet surfaces before assembly; optional; use on a surface you can wipe

Steps

1. 1

   Set the scale together

   Sit with your child and look at the reference sheet. Point out that Jupiter is about five times as far from the sun as Earth, and Neptune is about sixty times farther. Together, decide on a scale: if Earth's orbit arm is two inches long, what does that make Neptune's arm? Let your child do the multiplication. Write the arm lengths down before you start cutting.

   Tip: A scale where Earth is 1 inch from the mast and Neptune is about 30 inches works on a large table; adjust if your table is smaller.

2. 2

   Build and stand the mast

   Have your child tape the cardboard tube upright in the center of the cardboard base. Three strips of tape from tube to base, spread around the circumference, hold it stable. If the tube wobbles, tape a triangular cardboard gusset to one side.

   Tip: A heavier base — two layers of cardboard taped together — prevents the whole thing from tipping when outer arms are added.

3. 3

   Shape and attach the arms

   Cut or bend eight pipe cleaners or wire lengths to the arm lengths you calculated. An adult should close any sharp wire ends with pliers or tape before handing each piece over. Your child then tapes each arm to the mast at slightly different heights so the strings do not tangle — stagger them in a spiral up the tube.

   Tip: Going from shortest arm (Mercury) at the top to longest (Neptune) at the bottom keeps the model from looking top-heavy.

4. 4

   Make and color the planets

   Your child crumples eight pieces of scrap paper into balls of graduated sizes — Mercury small enough to sit in a fingertip, Jupiter about the size of a golf ball. They color each one with washable markers or watercolors: red-orange for Mars, tan-beige for Saturn, deep blue for Neptune. These do not need to be exact; the differences in size and color are what matter.

   Tip: Let the watercolor dry before hanging — five minutes is usually enough.

5. 5

   Cut and attach planet strings

   Your child cuts eight lengths of string — these can all be the same short length, since the arm handles the distance. Have them tape each string to the top of a planet ball, then tie or tape the other end to the tip of the corresponding arm. The planet hangs freely below the arm tip.

   Tip: If a ball spins and unwinds, a second small piece of tape holding the string to the side of the ball stops the rotation.

6. 6

   Check the order and finish

   With the reference sheet beside you, have your child check that the planets are in the right order outward from the mast: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Make any swaps needed — it is a simple matter of reattaching a string to a different arm. Your child labels each planet with a marker directly on the ball.

   Tip: Asking 'which planet is missing?' rather than pointing out the error gives your child the satisfaction of catching it themselves.

Take it to the table

Materials checklist, the steps and the variations on one Letter page.