Proving the shape of the Earth

Well this is a few days later than I wanted it to be due to a combination of exams and my house-mates dragging me into various LAN games but as promised a post about how to prove the earth is spherical-ish even with 2000 year old technology. But before that here is an article I found a few days ago that would have gone nicely with my previous post.

The first and simplest to argue evidence would be launching into space and seeing for yourself, a few orbits should convince anyone but that's not an economically sound idea and certainly wasn't possible 2300 years ago when the idea first cropped up. A less impressive alternative would be to look out over a vast flat landscape from a plane or high mountain, they would also put you high enough to see the curvature of the Earth.

A more intellectual argument was proposed in the early 1600s when two important details had been understood, first the heliocentric system proposed that the sun is at the centre, thus the Earth is another planet. Second, with the invention of telescopes moons were seen around Jupiter showing the other planets were spherical (and later on sufficient detail was possible to directly see the planets rotating and since they were circular at all times spherical), so Earth probably is as well. Not entirely satisfying but a nice piece of logic none the less.

Another interesting argument comes from an understanding of gravity, the net attraction of a body pulls an object towards its centre of mass, thus if you have a ball anything on the surface is pulled directly into the surface but if you have a disk objects near the edge are pulled sideways with only a small downwards component. We have all herd stories about falling off the edge of the world but who has herd about magical forces dragging people back towards the centre or (since they would assume gravity was still directly down)land that keep getting steeper until it is unclimbable. Another interesting effect would be that all the water on the Earth would be pulled into a partially flattened dome over the centre.

Now for some ancient direct observation, if you were to climb a mountain(the higher the better) near a plain or the ocean and look out over it there would be no obstacles so on a flat earth you would be able to see to the next mountain range or the edge of the Earth, whichever came first. That doesnt happen and since it was possible to observe people coming from distant lands from the top of the mountain long before they were visible from the bottom of the mountain the Earths surface is clearly curved. The increased elevation would allow visibility of a greater proportion of the surface (put a blob of blutac on a football then keeping your eye as close to the ball as possible turn it until the blob is no longer visible. Then move your head directly away from the ball and it will become visible) but it is possible to go one better than that. If you know the height of the mountain and take a protractor to the top then measure the angle from horizontal to the horizon it is just a case of simple trigonometry to find the radius of the Earth. This method is so effective that in the Masudi Canon, Abu Rayhan Biruni(973-1048) calculated the radius to within 16.8km of todays accepted value. That was about 600 years before the Western world was even in the ballpark.

a few more proofs

website of the flat earth society, all the arguments are flawed in premise, logic or what it would mean but its kind of interesting. If you cant spot one of the mistakes ill be happy to point it out.

As always anything you don't understand, want to clarify or think is incorrect either research it yourself or comment and even if its years from when I wrote this ill get back to you as soon as I can. After all "its better to be corrected and look the fool than remain ignorant and be a fool forever", can't remember who said it and its paraphrased but you get the idea.