You see images all the time of the Earth being round, you're told by the government, you're told in school. The horizon is apparently proof but I want the real truth. I want all the arguments, all the answers: everything.
Nobody will be able to give you everything.
Knowldege of the shape and place/role of the Earth was developed during last at least 2500 years,
as soon as ancient civilisations spread their travel, trade and land measure.
Maybe you could think of this:
Distance from pole to equator is 10 000 km, circumference of equator is 40 070 km.
If C = 2 * Pi * R, then why circumference of the equator is not 62 832 km?
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Meridian from pole to equator was first precisely measured in 18th century (and more later), when they defined meter as 10 millionth part of the distance from equator to pole.
They measured meridian through Dunkirk and Barcelona and determined the length of meter.
That is how we know that
Distance from pole to equator is 10 000 km.
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If you look at Flat Earth map (most common is Gleason's map or variation) and on globe, you will see that they have some things in common.
Longitudes match, latitudes match, distances along any single meridian match.
So, we can ignore shape of the Earth and use data independent from it:
Longitudes and latitudes as equal in both models.
Public records for ground distances (from neither model), already officially measured and verified through public use for military, commercial / industrial, roads, power and communication lines, governmental records on land and resources, or even timing and fuel consumption in transportation.
I already wrote before how we know the equatorial circumference:
"Find Jilib in Somalia, Kampala in Uganda, Mbandaka in Congo, and Libreville in Gabon.
Jilib: longitude - 42.78 degrees east
Kampala: longitude - 32.57 degrees east, distance from Jilib - 1136.5 km
Mbandaka: longitude - 18.29 degrees east, distance from Kampala - 1590 km
Libreville: longitude - 9.47 degrees east, distance from Mbandaka - 981.3 km
From Jilib to Libreville is 3708 km and 33.31 degrees of longitude.
It makes speed of solar noon to be 3708 / 33.31 * 15 = 1669.768 km/h.
That speed multiplied by 24 h gives circumference of Equator to be 40074.45 km
Ofcourse there is error.
Every measurement has errors.
But how big is our error?
Checking Equator circumference at shorter distances inbetween gives
Between Jilib and Kampala we calculate 1669.686 km/h, which gives 40072.48 km.
Between Kampala and Mbandaka we get 1670.168 km/h, giving 40084.03 km.
Between Mbandaka and Libreville we get 1668.877 km/h, which gives 40053.06 km.
All values are very close to each other. Our error is below 0.05% (below 500 ppm - parts per million).
Ok, we have that
Circumference of equator is 40 070 km."
