Flat Earthers says it's impossible to resolve shape of the earth. I disagree. There are 3 observatories south of the equator that cannot see Polaris(North Star). Why? Because it's blocked by curvature of the earth. Don't take my word for it, feel free to contact them yourself.
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Australia
https://www.assa.org.au/facilities/theheights/
South America
http://www.cassaca.org/en/
South Africa
https://en.m.wikipedia.org/wiki/Observatory,_Cape_Town