How to build a model solar system

 By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

06 April 2014

I gave a talk to class 8 pupils of the Nairobi Primary School recently. The title was “Sizing-up the Solar System”. It was an eye-opener for me: I was amazed at the level of interest that these young brains have in scientific matters. So, for the benefit of those in other schools, here is a summary of the talk.

We started with a model Globe of the World; the one that is commonly found in most schools. We measured its diameter and found it to be about 30cm. With that measurement, we asked the question: What would be the diameter of a model Sun draw in the same scale as that of the globe?

The first step was to determine the scale of the globe. This we found by simply dividing the diameter of the Earth (in kilometres) by that of the globe (in centimetres). Now that might seem like mixing oranges and lemons, but the aim was to find out how many kilometres are represented by one centimetre on the globe.

Thus we divided 12,800km by 30cm and found that one centimetre on the globe was equivalent to 427km on the ground. With that scale, we were now ready to work out the diameter of a model sun.

Now the real sun is 1,390,000km across. On the scale of one centimetre representing 427km, the diameter of the model would be 1,390,000 divided by 427. That is, 3,255cm; or 32.55m. As it turned out during the talk, such a model sun wouldn’t fit inside the 25-metre hall where we were assembled! We all agreed that building it wouldn’t be an easy task.

Nevertheless, we went on the next question: How far away would the model sun be using the scale of the globe? The distance from the real earth to the real sun is 150 million kilometres. To find the separation between the globe and the model sun, we divided 150,000,000 by 427. The answer is 351,000cm; or 3,510m; or 3.5km. Now, from Nairobi Primary School at Mamlaka Road, 3.5km will get you to the Capital Centre Mall on Mombasa Road!

Finally, we considered where the most distant planet (Neptune) would be. In reality, it is 4.5billion kilometres from the sun. Dividing 4,500,000,000km by 427 gave us about 10 million centimetres; that is 100,000m or 100km.

In summary, if the solar system was reduce to the scale of the model globe sitting at the Nairobi Primary School, the sun would be a 32m sphere at the Capital Centre and the farthest planet would be orbiting from 100km away – that is, an orbit passing near Sultan Hamud, Sagana, Naivasha, and Magadi.

In the end, I learned two things: first that children are eager to learn new things and second that our school syllabus is quite boring. Perhaps the next curriculum review should focus more on making knowledge interesting.