We have been studying astronomy this semester. A lot of what we have been looking at has been inside the solar system. Brief descriptions of the planets, the nature of eclipses, seasons, moon phases, that style of thing. One thing the books are never able to adequately describe is the sense of scale involved.
Douglas Adams once had a go in The Hitchhikers Guide to the Galaxy when he wrote this.
‘Space is big. Really big. You just won’t believe how vastly, hugely, mindbogglingly big it is. I mean, you might think it’s a long way down the street to the chemist’s, but that’s just peanuts compared to space.’
To try and convey this to the boys however, I felt we needed something a little more graphic. We were going to build ourselves a scale model of the solar system.
Our first step was to draw the sun and all the planets to scale. The scale I chose was 1 mm : 10,000 km. This meant that the inner planets were drawn as little more than dots, but the importance of this scale would come into play later on.
We labelled the planets and then taped them onto garden stakes. The main part of the lesson took place down at the beach.
In a similar way to how we used the beach as a timeline, we needed a lot of space to get the scale right. I could have just drawn the planets to a different scale to the distances I was trying to convey, but that is just what I was trying to avoid. When it comes to scale models, I tend to be a real stickler for accuracy.
Down at the beach, we used the sign at the base of the headland as our starting point. We stuck our sun on the sign, and then measured out the distances of the inner planets.
At this scale, the moon would be four centimetres away from the earth. We ended up putting them on the same label. Altogether, the inner planets made a relatively compact group.
Once we moved onto the gas giants, it became quite apparent just how far out the outer planets really are. By the time we made it to Neptune, we were 450 m away from our sun. If you look really carefully, you can see just see the sign we taped it to. In a sense, I am glad they downgraded Pluto from a planet, because we were only two thirds of the way there, and the boys were tired of walking up the beach.
At this scale, the Oort cloud would start at around 74 km away and extend to 1500 km, its outer edge marking the cosmographical boundary of the solar system. Proximal centauri, our nearest neighbouring star, would be at the very tip of Cape York peninsular, 3000 km distant.
Looking down the beach at our model, I was trying to ignore the scenery and focus only on the tiny specs we had drawn in these inconceivable amounts of emptiness. I don’t know just how much of this the boys were able to take in, but it certainly made an impression on me.
What a great learning activity! It does really make an impression to see it explained that way and to see the distances involved.