If you have the means and the will, you can personally measure the distances between different points on Earth (by travelling there yourself, not just looking at a map/globe someone else made). Then use geometry to deduce whether Earth is a sphere or not.
https://en.wikipedia.org/wiki/Surveying
I am neither a flat- nor globe-Earther btw, I consider myself to be agnostic on this issue
I don’t think it’s as simple as that.
Everything is ratios. Yes, the current numbers provided can justify a spherical earth. But I could also fill in my own, properly ratioed numbers that could justify another’s belief in a flat earth.
In all honesty, I’m probably more like you. I don’t claim to know what the world looks like because I’ve never been far enough away to see it in comparison. But I used to believe it was spherical. I no longer hold that particular belief.
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