Science Fenns K-5Grades K to 5
Three kids in a dim classroom with a lamp on a desk, one holding a small blue ball and a smaller white ball.

Science / All lessons / Sun, Earth and Moon

Model the Orbits

Build the three-body dance with a lamp and two balls.

Lesson 24 of 41

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Before we start

Today’s story

Model the Orbits

Space is too big to hold. You cannot put the Sun in a classroom. So scientists build models. A model is a small copy that helps you see an idea.

A lamp can be the Sun. A ball can be Earth. A smaller ball can be the Moon. Now you can watch them move in a dark room.

Every model leaves something out. Ours will not be to scale. The real Sun is far bigger and far away. Here are the steps.

See it

Five steps. Every time.

    Hands on

    Lamp and Ball Model

    30 minutes · Do this with a grown-up nearby

    You need

    • A lamp with the shade removed
    • A tennis ball or orange for Earth
    • A marble or small ball for the Moon
    • A pencil
    • A dark room
    • A paper and a pencil to record

    Do this

    1. Ask an adult to set the lamp on a table and plug it in.
    2. Turn off the room lights.
    3. Stick the pencil in the Earth ball to hold it.
    4. Walk the Earth around the lamp in a circle.
    5. Hold the Moon ball and circle it around Earth as you go.
    6. Watch which half of each ball is lit. Draw it.
    Write or draw: Draw your model. Label the Sun, Earth and Moon. Write one thing the model leaves out.

    Watch for: Notice that half of each ball is always lit by the lamp. Notice the lit half changes as you move.

    Safety: Only an adult plugs in the lamp. Do not touch the bulb because it can get hot.

    Same every time

    Three rules

    Rule 1Show the orbits.

    Earth goes around the Sun and the Moon goes around Earth.

    Rule 2Say what is left out.

    Every model has limits.

    Rule 3Move slowly.

    Slow motion makes the pattern easy to see.

    Grandpa Fenn’s notebook

    Say it like a scientist

    model
    A small copy or picture that helps explain a big idea.
    orbit
    The path an object takes around another object.
    scale
    How big something is compared to the real thing.
    limit
    What a model cannot show well.

    Poppy’s quiz

    Six questions

    Tap an answer. Green means right. You will see why.

    Talk about it

    Say it out loud

    • How do you know your model is a good one? What would you change?
    • What other things at home could stand for the Sun, Earth and Moon?
    Did you know

    If the Sun were a front door, Earth would be about the size of a dime, and far down the street.

    Someone who does this

    A planetarium operator builds models of the sky so people can explore it.

    BeforeSun, Earth and Moon OrbitsNext lessonThe Planets in Order