Earth and Moon's orbit to scale

Use an exercise ball as a Sun, then make the Earth and Moon from modelling clay to scale. Space the objects to scale across the school grounds and show how they orbit each other.
Science content
Earth/Space: Sun, Moon, Solar System, Universe (1, 4, 6)
Lessons activity is in
  • exercise ball, or other large sphere with a diameter about 60cm (circumference about 185cm)
  • modelling clay in green, blue, brown and white
  • ruler showing 15cm
  • large area where 63 metres can be paced out in a straight line

Before class, find an outdoor route extending in a straight line 63m long, from where the model Sun will be (the exercise ball), to where the model Earth and Moon will be. If a gravel field is used, an orbit path can also be traced on its surface.

In the classroom, show students the Sun (exercise ball), and tell them that if the Sun is this large, Earth is only 5.5 mm wide, and the Moon is only 1.5mm wide!
Distribute the rulers, Earth/Moon images and modelling clay to student pairs. Ask each group to make a model Earth (5.5mm in diameter) and Moon (1.5mm in diameter) from the modelling clay, using the image to guide their colour choice. Students will likely make them too large to start - prompt them to keep removing clay until they are the correct size. Invite students to bring their model Earth and Moon next to the model Sun (exercise ball) to demonstrate how much smaller our Earth is than the Sun. Emphasize that in the classroom, using these model sizes, we cannot place them at the correct distances from each other to show how far apart they are on this scale.
Take the students outside with the model Sun, Earth and Moons, as well as a metre stick/tape measure.
Place the Sun (exercise ball) on the ground, and tell students that, to scale, the Earth and Moon will be 63 metres away from this Sun! Lay down a metre rule/tape measure, so that students can roughly gauge how long their stride needs to be to pace a metre. Then as a class, pace 63m from the Sun. Place one of the Earths at this spot. Look back at the Sun to see how far away it is and how much empty space there is between the Earth and the Sun.
Then place one of the Moons 15cm from the Earth. Indicate how the Moon orbits in a circle around the Earth, one orbit taking one month. At the same time, the Earth is orbiting the Sun, moving on a path always the same distance from the Sun, taking one year to orbit around the Sun..

Object Scaled diameter Scaled distance
Sun 60cm (exercise ball)
Earth 5.5mm 63m from the Sun
Moon 1.5mm 15cm from the Earth

Optionally, trace out the orbit of the Earth in the gravel (or make a chalk line), walking around the model Sun but always staying 63m (or thereabouts) from it. Tell students that a season passes as the route takes you ¼ of the way around the Sun (then another season if you able to walk ½ way around the Sun). Complete as much of the orbit as possible.
Before heading back to the classroom, use the model to emphasize how far away the Sun and Earth are, and in turn how far the Earth and Moon are from each other, and how much empty space there is in-between.

As an alternative to placing one Earth and Moon, place the Sun, then ask students to pace 63m away, all in different directions, taking their model Earth and Moon. When the students each reach their spot 63m away, tell them to place their Earth. Then place their Moon, 15cm from their Earth. Each of the Earths show a different part of the Earth’s orbit around the Sun. Walk between the student groups, tracing a path if possible, to show the orbit of the Earth around the Sun. Tell students that while the Earth orbits the Sun, the Moon is also orbiting the Earth.

Grades taught
Gr 3
Gr 4