Since been involved in a couple of recent flat earth debates I’ve been more conscious of making observations of the horizon when the chance arises. A good opportunity arose on Saturday when I did a short detour over Tamborine Mountain in Queensland, Australia, which gives spectacular views of Australias Gold Coast from an elevation of 520m (1700 feet). While Admiring the view I noticed the horizon almost matched the tops of the buildings as you can see in this image I captured.
The building in the center which doesn’t quite reach the horizon is the “Soul” Building at 243m. At the right-hand side is the Q1 building which reaches 322m at the top of the spire, with the roofline reaching around 260m or so. Both buildings are very close to the waterline so the bases are perhaps 5m or so above sea level. Incidentally, these are the same buildings shown in my previous article but shown from the other side. The camera elevation is 515m with the distance to Q1 being 23.6km.
So why is it interesting that the horizon matches the tops of the buildings? The reason is that on flat earth the horizon would have appeared well above the tops of the buildings because the camera elevation (515m) was at nearly double the building tops. Hence we must be looking down towards the horizon, something that can’t happen on flat earth where the edge is 1000’s of km distant. Here is the image processed to show the horizon better (by extracting just the red channel, and boosting contrast).
The following diagram shows the viewing geometry.
Using this geometry and Similiar triangle it is easy to show that if the earth was flat the horizon would appear much higher than the tops of the buildings. Even if the “Edge” of the flat earth were just 100km from the camera, the horizon would have still appeared higher than the 322m mast of the Q1 tower (which it clearly doesn’t). Having flown over the Ocean in that direction towards New Zealand I can vouch for that edge would have to be over 3000km away, and therefore a flat earth horizon would have to appear at a level close to twice as high as the buildings.
So this is where the horizon would appear in the images if the earth was flat. I’ve used an edge filter to bring out the edges in the image. But I think you can see that the observed horizon is much too low for a flat earth, so clearly the earth is dropping away in the distance. Technically, this does not prove the earth is a globe (just supports it) but precludes flat earth.
Here is the more standard view, showing where the theoretical flat earth horizon should appear.
A common argument that would be used by flat earth proponents is that refraction is altering the position of the horizon. The problem with this argument, however, is that refraction will actually make the horizon appear higher than it is. Therefore, if I had factored atmospheric refraction in the above diagram the flat earth horizons would appear even higher than shown. In reality on a flat earth, there would be no horizon, as atmospheric extinction would mean there would be no clear distinction between the sky and ground.
In conclusion, it is very easy to confirm the earth is not flat using just your own eyes and armed with some basic geometry knowledge.
