When I heard a loyal listener to the BBC’s More or Less podcast recently ask, “which planet is Earth’s nearest neighbour,” I honestly thought I knew the answer already. How wrong I was! As a teacher, I know all about ‘growth mindset’, so I am prepared to admit that I am poorly educated about our solar system (and I was lucky enough to have the opportuntity to study an Astronomy course at University a while back – even worse!).
Could my ignorance have had anything to do with unhelpful diagrams like the one below? The word ‘model’ has many meanings, but here we are talking about “a representation of current understanding”. For example “the model of gravity in the 19th century did not include quantum effects.”
What do you think is wrong with the ‘model’?
Let me first say I really like this image as a ‘poster’. In fact, having this kind of awe-inspiring scene displayed on classroom walls, gave me a great deal of relief and pleasure when I was bored in lessons, and probably made my teachers’ lives far easier. It gives an idea of how the planets appear visually, with all their wondrous rings & storms, and also shows their approximate relative sizes. No moons, but I guess they would have cluttered it up.
This beautiful image undeniably makes a dramatic and memorable impact, but because it is such an over-simplification, it might actually hinder our capacity to think accurately in geometrical terms about our star system. Can anyone really have a intuitive ‘feel’ for distances greater than the size of our planet?
Personally, I think I need accurate pictures to help my little brain reach up to such massive proportions.
Scale models show us the somewhat uglier truth!
Take a look at this image of a model of the Sun-Venus system made in Geogebra, which is actually drawn to scale (Mercury is the closest planet to the Sun).
QUESTION: The actual distance is about 58 million Km – can you figure out what scale this model uses?
ANSWER: So 58 million Km or 58 000 000 Km is shown by 5800 units. So 1 unit on the axes represents 10 thousand Kilometers in real-life. Roughly!
Take a look at the following image of a scale model showing the Earth with our Moon orbiting around us.
QUESTION: How many planet Earth’s do you think could fit in between Earth and the Moon?:
ANSWER: Earth’s diameter is 12 742Km (WIKI); Earth-Sun distance is 384 402Km;
384402 / 12742 gives us about 30, so 30 planet Earths could fit side by side in the gap. This would look better in Latex!
Finally let’s take a glance at 3 images of a scale model that includes Earth, Moon and eventually the Sun. We’ll start focused on the Earth & Moon and gradually pull back to show how far away the sun is relatively . I apologise in advance – it’s kind of hard to see, but I will include links to the Geogebra applets below so you can go and explore at leisure.
The actual Solar System is far less photogenic!
Have you seen any other ‘educational’ images that might be conceptually misleading?
Please submit a comment below with a link to the image in question.
My sincere thanks for reading folks!
- Sun, Earth and Moon to scale in Geogebra