I have an algorithm I believe will prove to any flat-Earther that they're wrong (referring to proof within reasonable limits, and not mathematically formal proof).
1. Select a meridian line of the Earth where simultaneous observations can be made by two individuals (or instruments), where one is located on the meridian in the northern hemisphere between 30-60 degrees latitude, and the other is located on the same meridian in the southern hemisphere between 30-60 deg latitude. Try to locate them on the same latitude line - as closely as possible - for their respective hemispheres.
2. Place a camera at these locations (a human can operate the camera or they may be automated). The cameras should be identical, wide-field, and they should be oriented at the same angle with respect to the ground to capture the night sky directly overhead.
3. Take a picture with both cameras at midnight.
4. Compare photographs.
5. Realize that the night sky is different at the two locations.
6. Prove that the surface of the Earth is curved.
The reason this will work is based on simple math.
The choice to use an identical meridian line is not affected a priori by the roundness or flatness of the world, and would work in principle whether either was the case.
If the photos have different features in the night sky, the only possible explanation is that the Earth is curved. That is because if they are different, it can only mean that each camera is on a unique tangent line to the Earth's surface.
The only thing that can have multiple non-trivial tangent lines is a curve.The degree of overlap between the two photos should decrease with increasing curvature.
P1. If the Earth is flat, very different photos should not be possible.
P2. Very different photos are possible.
C. Earth is not flat.
If this is explainable under Flat Earth, please educate me.
EDIT: including a couple diagrams to communicate the hypothesis visually
https://files.catbox.moe/b86utk.jpeghttps://files.catbox.moe/41dsf5.jpeg
