Lately, I have become a fan of some YouTube channels that take on the belief held by some that the earth is flat. I have enjoyed watching SciManDan, PlanarWalk, and Dave McKeegan all debunk this long-past-due-for-the-dustbin-of-history conspiracy theory.

There is a certain fascination I have in watching these videos, not the least of which is the desire to see people who are so obviously wrong proven to be so. The problem is, there is no proof that can convince a Flat Earther—they deflect, change the topic, or simply refuse to believe that the evidence you provide is legitimate. They do this not just with pictures and video taken from the International Space Station but even with the evidence that they themselves have come up with. For example, in 2019, some Flat Earthers bought a $20,000 laser gyroscope to prove that the earth was not rotating. When their experiments showed that there was a 15° drift every hour (precisely 1/24th of 360°) they simply refused to accept the results. When they created a second experiment to show that there was no curvature, and it, too, showed that there was, the experimenter simply remarked, “Interesting,” but didn’t concede that he’d been wrong.

And so, as I have watched these videos, I keep looking for the knockout blow—the piece of evidence that makes it impossible for the earth to be flat, the result that even the most hardheaded, stiffnecked Flat Earther could not ignore. Now, there is plenty of evidence that does this, but a lot of it requires some understanding of science or math, which are often not the strong suits of the Flat Earth set.

I kept wondering what evidence could possibly convince such a person, short of a ride into space on a rocket (a trip I would gladly pay for if I had the means—one-way, of course). And then I came across the following photo:

This photo was taken by Kevin Jackson of Birkdale, Southport, England, of the city of Blackpool, some 18.51 km (11.49 mi) away on a particularly clear and beautiful day. The photo became a viral sensation and has been used to raise money for charity. But it also irrefutably disproves any notion of a flat earth.

See, given the respective heights of the Blackpool Tower (158m/518ft) and the Dow Crag peak just to its right in the background (778m/2552ft), the mountains in the back should loom over the tower in the foreground. But that’s not what happens; the tower clearly appears higher than the mountains in the background for a very important reason—the base of the mountains is actually below the horizon because of the curvature of the earth.

Unlike photos from space, which are disbelieved by Flat Earthers and hard to produce on your own, this one was a chance photograph taken by a photographer using a Nikon D750 with a good telephoto lens. In other words, this is a picture anyone could take with a decent camera.

And so, with this photograph, I set out to see if it would be possible to graph how this photo disproves the Flat Earth. There are proofs I have seen online that involve various tables, charts, and formulas, but I wanted something more visual.

Finding the Numbers

The first thing I had to do was get accurate measurements of the distances involved. I used mapmyride.com, a site I frequently use to plan, map, and record bike rides. The mapping software usually follows road or bike trails, but you can configure it to draw straight lines. And so, with that tool, I drew a straight line from the peak of Dow Crag in the Lake District to Blackpool Tower and then on to Southport. I measured 61.95 km (38.5 mi) from Dow Crag to Blackpool and another 18.51 km (11.49 mi) from Blackpool to Southport. The total distance from the top of Dow Crag to the location of the photographer was 80.46 km (49.99 mi).

Then I measured the relative height in pixels of the tower and the mountain. The 158m-high tower was 82 pixels high, and the 778m-high mountain in the background was 60 pixels high.

Mapping It Out

Now that I had all the relevant information, all that was left to do was to graph out the relationships between the objects: the mountain 80.46 km away, the tower 18.51 km away, and the photographer. I would graph these objects and distances assuming a flat plane; after all, if the earth were flat, this is how the objects would be arranged.

This proved to be more challenging than I expected—not because the task of plotting was terribly difficult but because the scale was hard to fit in a format that would be readable. It turns out that 80.46 km is really far and dwarfs an object that is 778m high by a factor of over 100. But with the right graphing tools and an appropriate scale, I was able to plot the objects on a graph.

On the graph, each block represented 200 m with five blocks per kilometer and a total of 402.5 blocks for the entire distance. At this scale, a 158m-high tower would be 0.75 blocks; the 778m-high mountain, 3.75 blocks.

Now that the scale was worked out, all that was left was to map out the distances and see where the respective sightlines should appear to the observer in Southport:

After mapping out the tower and mountain with their heights and distances to scale, I traced a sightline (in red) from the top of Dow Crag (778 m) to the observer (2 m).

An interesting thing happens as that sightline passes Blackpool Tower—it goes over the tower. If all the objects were indeed on a flat plane, then even with the effects of perspective at a distance of 80.46 km away, Dow Crag should appear taller than Blackpool Tower, only 18.51 km away.

But that’s not what we see in the photo—in the photo, the mountain appears substantially lower than the tower—27% lower, in fact. If the 158m-high tower is 82 pixels, then a 60-pixel-high mountain should have an apparent height of 115.6 m.

And so, I traced a line (in green) from the observer that would cross Blackpool Tower at a height of 115.6 m and followed it out to the 80.46 km mark. An interesting thing happens: the top of Dow Crag comes in at around 400 m, with another nearly 400 m below the horizon (the solid black line).

So there you have it—an impromptu photo taken on a clear day provides the most definitive photographic proof—short of taking pictures from orbit—of the curvature of the earth.

Definitive Proof

I would like to think that this would have to convince even the most die-hard Flat Earther, but I know better. Their beliefs aren’t rooted in reason, they’re rooted in distrust of authority and a feeling that they’ve been misled, among other reasons that I’ll explore in a separate essay.

But in the meantime, it is satisfying to know that even using a simple method like this can confirm the basic nature of reality. And after spending so long watching Flat Earthers make their cockamamie arguments, it’s comforting to know that I haven’t been completely driven mad as a result. Reality is still there, and you can go out and take a picture of it.