Modelling the solar system

Forget the mind-boggling nature of the universe, just the Solar System is almost unimaginably huge and unimaginably empty. No textbook image or poster on a classroom wall can even begin to capture this. Surely, an awareness of the minuteness of our existence in the immensity and eternity of the cosmos, is a cultural entitlement, a perspective on life, that all children should be exposed to.

Unlike ecology, there’s not much call to go outside the classroom for physics. Apart from pure entertainment (water rockets) my list is:

  • Measuring the speed of sound;
  • Modelling refraction;
  • Modelling the Solar System.

Modelling the Solar System can either be a chaotic time-waster or quick and effective. This is my approach. #nobogpaper

Use this calculator to get yourself sorted with suitable ‘planets’ and distances. This is my list. Obviously you can do some rounding. Ball bearings look nice, are cheap and easy to order, and last forever if you keep them dry in a little pot. But get a few. Children can have butter fingers and they’re hard to find in the grass. Dried peas and things are another option.

BodyDiameter / mmModelled withOrbital radius / m
Sun800Beach ball – ish
Mercury2.7Ball bearing33
Venus6.9Ball bearing62
Earth7.3Ball bearing86
Mars3.8Ball bearing130
Jupiter82Hockey ball450
Saturn67Tennis ball820
Uranus27Marble1600
Neptune26Marble2600

The Sun is a bit of a pain. I’ve got a big yellow cardboard circle that folds up, that a technician made for me years ago – a beach ball will do although it’s probably a bit small.

Sort your distances in advance. You can just pace them out roughly but don’t do it live (or at least not the longer ones) because it’s too easy to lose count whilst dealing with behaviour or a question or something. Obviously you’re not going to do them all but if you’ve got a playing field long enough to get somewhere near Jupiter, that’s good. Use permanent markers like “in line with that tree”, or “about 30 m past the corner flag.”

In the lesson, obviously you need to think about the sequence leading up to this activity, like the Sun as a star, what the Solar System is (and that it’s not unique – hello Kepler, TESS, and the James Webb Space Telescope), making sure they’re clear it’s heliocentric, My Very Easy Method Just Speeds Up Naming (planets), and some ideas about small/rocky v gas giants and stuff, but apart from all that, here’s how I would run actually modelling the Solar System.

“When we look at an image like this (projected image of Solar System, or textbook page) it shows what the planets look like quite well. But it can’t show the huge distances between the planets because the screen/page isn’t big enough.”

“If we can’t make measurements off a diagram, we should include a label. This is a vote. Point that way if you think we’d normally say ‘Scale not accurate’, point this way if you think we’d normally say ‘Not to scale’. 3, 2, 1, point! Sophie, any thoughts where else you see that?” (Might be other good suggestions but I want them to link to maths). “And what does it mean again?” (Can’t take measurements off the diagram).

“Now we’re going to try to do the Solar System to scale. Here’s the Sun in our model. Get ready to show me with your fingers or hands how big you think Earth is to the same scale – 3, 2, 1 show me!”

“Right, here’s the Earth to scale.” Show them. Some children in some classes go overboard on the woo-ing at this point. I’ve mistaken arsing around for engagement in the past. Now I’d just be explicit if they over-do it, “It’s fine to say ‘oh, wow’, or make a quiet noise to show you’re surprised. It’s not okay to exaggerate or be silly or be loud. The consequence for doing that again is [school policy].”

“Let’s try Jupiter, it’s a gas giant and the largest planet in our Solar System (or cold call this if you did it earlier). Here’s the Sun, here’s Earth. Get ready to show me with your fingers or hands how big you think Jupiter is to the same scale – 3, 2, 1 show me!”

Repeat for Mercury.

Then dish out the ‘planets’ (Sun to Mars to children you can trust, and they will need to be a bit a bit more independently capable because they miss out on a bit of spiel).

“We are going to make a scale model of the Solar System. We are going to do this to scale so you can see what it really looks like. To have enough room we have to go outside but even then we will have to have the planets all lined up whereas they are normally all at different points around their orbits”. It’s good to have two images up to match this explanation.

Now I’d give them the pep talk about behaviour, tell them where to go first, make someone the leader, stand at the door and make them file out past me following the leader, lock the lab, catch them up and stop at the Sun position.

Don’t beat about the bush. Just drop off one or two children with the Sun and tell them not to move until you come back. Take everyone else across the field quickly dropping off Mercury, Venus, Earth and Mars as you go. Make them hold up their planet. Get to Jupiter’s position and put the children in a semi-circle looking at Jupiter and you with the inner planets behind you.

“This is the Solar System to scale. Look how tiny the planets are compared to space between them. Think how small people are on the Earth in the vastness of space.”

“Who has Saturn. Hold it up. We’ve run out of room but we would have to go almost as far again from the Sun to put Saturn in the right place. Who has (hold of) Uranus [which fool named that planet!]…, Neptune…”. Use some place they’ll know like Neptune will be in the Tesco car park. Give them a few seconds to think about the vastness of space and march them back collecting to the Sun, collecting everyone on the way and straight back to the classroom. No faffing. The true scale is immediately obvious and striking. Choices about discussion and further teaching or activities are optional but do them back in the classroom if you’re doing them at all.

That’s it. Don’t let it take too long.

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