"If the Earth is that tiny, imagine how small we are," my Year 3 student said, as he studied the ping-pong ball representing Earth in our scale model of the planets. It was as if, in that moment, he had realised the vastness of the universe. Suddenly there was an air of awe and wonder in the maths classroom.
With Earth Day approaching, we had decided to model the planetary system in the school hall. First the students selected and labelled their planets, drawing on data about their relative sizes. They then had to match them to a range of spheres we had collected for the purpose. They knew that Mercury has a diameter of 4,900km and could see from the data table that this was the smallest planet. So Mercury was represented by the smallest ball bearing. Earth, which is two and a half times bigger, was shown with the ping-pong ball.
Once they had labelled the basketball "Jupiter" to complete the set, the children began to work out how far each one should be from the Sun.
Another data table showed them the distances of each planet from the Sun - so far just a label on the hall floor. By using rolls of toilet paper as "non-standard" measures, the students worked out that if Mercury were one sheet of toilet paper away from the Sun (about 12cm) then Neptune, the furthest planet from the Sun, would be 77.5 sheets of toilet paper in the distance (about 9.3m).
Five different versions of the planetary system were laid out in the hall, so we took a walk among the planets to see each other's models. It was at this point that one group realised they had simply arranged their planets from smallest to largest away from the Sun: a very well ordered universe but not the one we live in. They quickly rearranged their planets and then we discussed how we could represent the Sun.
Using our rounding and estimating skills, we calculated that the Sun is about 10 times the diameter of Jupiter, the largest planet. It is more than 100 times bigger than Earth, which blew several small minds and three or four bigger ones, too. So we needed to create a sphere with a diameter of 2.25m to represent the Sun. Coincidentally - and delightfully - each group could model this sphere by joining hands in a circle to form the Sun at the centre of their universe.
After the lesson I talked to one of my own children, now 27, about how effective it had been. She laughed and told me that she still remembered making her own model of the solar system at primary school: it was one of her favourite lessons. Let's hope some of these Year 3 students are still talking about this lesson in 20 years.
Tony Cotton is a writer and author of Understanding and Teaching Primary Mathematics. These sessions were planned and delivered jointly with Rachel Parkinson, maths coordinator at Hunslet Moor Primary School, Leeds.
Sid the Spaceman has lost his rocket boosters - can your pupils draw some new ones to get him home? Recap astronomy with this 10-minute worksheet activity from bexibb. bit.lyAstronomicalArea
Try vicbobmac1's space-themed maths puzzles and activities, including intergalactic football and planet mazes. bit.lySpaceThemedMaths.