Why would anyone (500 to 1,500 years ago) believe in and teach Earth is a Sphere after viewing this horizon (below) everywhere they went for most of their life? What was the life changing evedience?
Hi Platt, apologies for the delay, first post. Been trying to register for a couple of days.
Firstly genuinely like your question, I love any question that makes you think and question any assumptions being made.
So I thought I would try and answer your question from a personal perspective, civil engineering, on how I would prove the curvature of the earth.
Within your timescale 500-1500 years ago I would be relying on arguments already presented, objects sinking into the horizon, observations of lunar eclipses, expanding my field of view with elevation, thought experiments regarding observing stars but not bright lights from distant cities, seasons, if I was able to travel extensively the differences experienced travelling through time zones, sunsets, star movements and the orbits of the visible planets.
Why would I be looking at things this way seeking answers, well the theory of the globe had been proven over 2000 years ago, Eratosthenes, and the first globe model appeared shortly after that, Crates of Mallus. The theory was hypothesised long before that, then proven and generally accepted via Eratosthenes experiment. What was discussed for a millennia after that was whether the earth or the sun was the centre point around which everything went around.
So looking at what had come before me I would have the principle of a round earth, my own observations and a number of proven experiments. But I still would not be able to demonstrate that physically to you myself, if you popped up and asked me.
I can only go back 469 years before I could do that, with the invention of the theodolite. Admittedly the 16th century theodolite is pretty crude, the mid 18th century model is the breakthrough, a design still found in modern mechanical theodolites.
Pretty crude but still workable. A lot of hard work based on the increased number of instrument moves required, sadly no telescope on my early theodolite, but topographical surveying is born.
Theodolites measure both horizontal and vertical angle using the same instrument. So i can set up a topographical survey, probably using a single line loop traverse, to check for errors in my measurements. Then I can both give an xyz to any point within my survey, triangulation had been invented 20 years prior to the theodolite, but also measure the angle if my start and furthest point.
Taking the angle measurements I can plug them into Eratosthenes experiment and not only replicate it but provide a more accurate answer.