The Earth is bigger than you can imagine!

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

01 March 2020

I still remember what my primary school teacher said as he tried to explain how large the earth is: “it is so big that you cannot even form its image in your mind!”. And he challenged us to close our eyes and try. Now where did these kinds of teachers go?

Of course, the reason you cannot form the image of the earth in your head is that you have never seen it in its entirety. You only see a small portion going out to only 5km on a flat level surface – for example when looking out at the sea.

You can see farther if you are standing on high ground; or you are at a low place and you are looking at tall mountain. For example, from the top of Mt Kenya, you can see the Indian ocean 500km away and Mt Kilimanjaro is visible from Machakos, 200km away.

These distances are very small compared to the size of the earth. If you were to travel all the way round the planet, you would cover a total of about 40,000km. But, unfortunately, such a journey cannot be done on the surface.

While a ship on the sea can travel on a straight path, it will encounter land and the traveller must alight to continue with the journey. Travelling on land has many challenges that make impossible to continue straight over long distances (thousands of kilometres).

Even flying in an aeroplane is not easy. The aeroplane that travels the longest distance without needing to refuel is the Airbus A350. It covers about 18,000km. That’s, literary, just “half way around the planet”.

Using an aeroplane, one may pick out four airports (say, Nairobi, Brisbane, Lima, Rio de Jeneiro and back to Nairobi) and fly from one to the next in straight paths, noting carefully distances and the change in direction of flight at each point.

These distances and directions are then plotted to scale on a piece of paper and total straight distance around the planet determined. It is quite easy in principle!

However, this is not how the circumference of the planet is measured. In fact, the size of the earth was first measured over 1,500 years before the first circumnavigation.

Greek mathematician, Eratosthenes, measured the earth’s circumference in 240BC by looking at the length of the shadow formed by a tall vertical pole. From some elementary geometry, he deduced that the distance is 46,100km – an error of just 15 per cent!

The important point to take away here is that, the basic geometry that many people ignore at school (Pythagoras theorem, sines, cosines, tangents, etc.) can help in determining some very important information.

Even if you may not need to know the circumference of the earth, you might want to build a fence in you plot of land in a way that forms a right angle. Pythagoras theorem comes in handy!