We have known for thousands of years the earth is a sphere! RIght?

We have known for thousands of years the earth is a sphere!
RIght?
....
Right guys?
Do you know HOW some guy 2000 years ago proved the shape of the earth?

https://publish.obsidian.md/shanesql/The+Circumference+of+WHAT%2C+though

Well...what actually happened was someone measured the CIRCUMFERENCE of our VISIBLE RADIUS. And told everyone with zero evidence that this applied to the physical globe earth that we stood on.... when it would be optically identical in either case.

This circumference is all that has EVER been measured, but the real question is,

THE CIRCUMFERENCE OF WHAT?

The physically curving ground that you have never seen and has never been measured by any human, ever. period.
OR....
The naturally curving celestial hemisphere?

Which, again, residents of both models agree is inherently curved, and both treat it as such.

It seems the circumference of the circle gets repeatedly measured, but how, in any of these instances, could you differentiate it being the circumference of a planar circle inside a sphere, or the circumference of the visible radius around you into the celestial heaven the same amount in every direction? [Which is also supported by Angular Resolution limit/aperture/wavelength of light/ diameter arguments for an optically curving planar earth]

one from the other from inside?? (See animation below)

What about that measured angle of the light would be different in a spherically curving earth, or an optically curving planar one?

Well there goes the whole basis for the globe !

"What!? You don't subscribe to the theory that 2000 years ago some dude assumed parallel light rays (against every observation) made a measurement of the angle of the sun, made a comparison to a known distance between two cities, then used the angle of the second observation to conclude THE WHOLE WORLD IS TILTED
D AT 23.4 Degrees? Since light beams from the sun that appear crepuscular are simply a trick that make it appear as if they aren't parallel.

Eratosthenes, a Greek astronomer, and mathematician, measured the circumference of the Earth around the 3rd century BC. His method involved measuring the angle of the sun's rays at two different locations at the same time. Here's a step-by-step explanation:

Understanding the Setup:

Eratosthenes used two cities: Alexandria and Syene (modern-day Aswan), which are approximately 800 km apart.
He observed that at noon on the summer solstice in Syene, the sun was directly overhead (no shadow cast), while in Alexandria, it cast a shadow, indicating the sun was at an angle.
Measurement of the Angle:

In Alexandria, he measured the angle of the shadow, which was 7.2 degrees. This angle is the central angle corresponding to the arc of the Earth's surface between the two cities.
Calculating the Fraction of the Earth's Circumference:

The 7.2 degrees is 1/50th of a full circle (since 360 degrees / 7.2 degrees = 50).
This means the distance between Alexandria and Syene (800 km) represents 1/50th of the Earth's total circumference.
Quantifying the Circumference:

To find the total circumference (C) of the Earth, we use the formula: C=Distance×360∘AngleC = \text{Distance} \times \frac{360^\circ}{\text{Angle}}C=Distance×Angle360∘​
Plugging in the values: C=800 km×360∘7.2∘C = 800 \text{ km} \times \frac{360^\circ}{7.2^\circ}C=800 km×7.2∘360∘​
Simplifying the fraction: C=800 km×50=40,000 kmC = 800 \text{ km} \times 50 = 40,000 \text{ km}C=800 km×50=40,000 km
Summary
Eratosthenes' measurement was based on the following principles:

The difference in the sun's angle (7.2 degrees) between two locations.
The known distance between the two locations (800 km).
Using the proportion of the angle to the full circle (360 degrees) to determine the Earth's circumference.
His method provided an estimate for the Earth's circumference that was remarkably accurate for the time, giving a value of approximately 40,000 km.

This of course applies to a circle as well as a sphere, especially defined by an that equation calculates the radius of a circle based on the angular resolution and the distance to the horizon.

R = d / tan(θ)
Where:
R = Radius of your spherical vision limit
d = Distance to Horizon
θ = Angular Resolution Limit

Eratosthenes used the cities of Syene (modern-day Aswan) and Alexandria in his famous calculation of Earth's circumference. Here are a few other city pairs and distances that could work similarly for measuring the Earth's circumference using a similar method:

City Pairs and Distances
Los Angeles and San Francisco, USA

Approximate Distance: 615 km (382 miles)
Both cities lie roughly on the same longitude.
Cairo, Egypt and Alexandria, Egypt

Approximate Distance: 180 km (112 miles)
Both cities are on a similar longitude and relatively close, making measurements easier.
Berlin, Germany and Hamburg, Germany

Approximate Distance: 290 km (180 miles)
Both cities are relatively close and on a similar longitude.
New York City, USA and Washington D.C., USA

Approximate Distance: 330 km (205 miles)
These cities are relatively close and roughly aligned north-south.
Beijing, China and Tianjin, China

Approximate Distance: 120 km (75 miles)
Both cities are on a similar longitude and relatively close.
Tokyo, Japan and Yokohama, Japan

Approximate Distance: 30 km (19 miles)
Both cities are very close and aligned north-south.
Madrid, Spain and Valencia, Spain

Approximate Distance: 350 km (217 miles)
These cities are relatively close and roughly aligned north-south.
Sydney, Australia and Newcastle, Australia

Approximate Distance: 160 km (99 miles)
Both cities are on a similar longitude and relatively close

Other stuff about the same:

Eratosthenes

https://www.youtube.com/watch?v=E-YBmX5a3qM&t=3702s

How do we know the Circumference of the limit of our vision?

https://www.youtube.com/watch?v=94xP53vbPQs&t=4s

DEBATISM X Ep X11: Roohif vs. Shane St. Pierre | Curvature: Optical or Physical?https://www.youtube.com/watch?v=VKgcMOhzNO4&t=3s
https://www.youtube.com/watch?v=2qz2yJWvvxc&t=49s Circumference of the Spherical Limit of your view

What did he measure? https://www.youtube.com/watch?v=9RShOAFh8JE

The Truth about Cryptosthenes, Eratosthenes, and the circumference... of what?
https://www.youtube.com/watch?v=DY72Op537nk