Do you believe earth curvature can be measured, and, if so, how?

[ZNP]

I think this is an effect of perspective. Like if you look at street lamps at a far enough distance, the furthest ones will appear to be at eye level. They're not - it's just that's how they appear because of perspective. Say, measure a street lamp at 1m horizontal distance, it will be close to 90 degrees. Then at 10m - less. By the time you get to 100m, it will likely appear to be close to eye level. It's not, and it's nothing to do with curvature given the short distance - it's simply perspective.

Earth's circumference was first accurately measured more than 2,000 years ago by the Greek astronomer Eratosthenes, who at the time lived in the Egyptian city of Alexandria. He had heard that in the nearby town of Syene midday sunlight shines straight down to the bottom of deep wells on the same day each year, indicating that the Sun was directly overhead in Syene. In Alexandria, however, sunlight on that date never reached the bottoms of wells, but instead fell upon the sides.

Eratosthenes reasoned that the difference in the angle of incoming sunlight was due to the curvature of Earth's surface, and so by measuring this angle, he related the distance between Alexandria and Syene to the total dimension of the globe.

On the day the Sun shone on the bottom of the wells in Syene, Eratosthenes measured the Sun's position in the sky over Alexandria. It was seven degrees away from the zenith, meaning Syene must be seven degrees away from Alexandria as measured on the circle that is Earth's circumference. Because seven degrees is about one 50th of a full circle (360 degrees), Eratosthenes simply multiplied the distance from Alexandria to Syene -- believed to have been about 515 miles (830 km) -- by 50. He calculated Earth's circumference at 26,000 miles (42,000 km), only five percent away from the modern accepted value of 24,901 miles (40,074 km).

https://stardate.org/astro-guide/faqs/how-was-size-earth-first-measured#:~:text=On the day the Sun,circle that is Earth's circumference.

I would also add that for thousands of years man has been using a sextant to measure the angle of the Sun so they could know their latitude and find themselves on a map of the Earth.

 

[Moses_Young]

Earth's circumference was first accurately measured more than 2,000 years ago by the Greek astronomer Eratosthenes, who at the time lived in the Egyptian city of Alexandria. He had heard that in the nearby town of Syene midday sunlight shines straight down to the bottom of deep wells on the same day each year, indicating that the Sun was directly overhead in Syene. In Alexandria, however, sunlight on that date never reached the bottoms of wells, but instead fell upon the sides.

Eratosthenes reasoned that the difference in the angle of incoming sunlight was due to the curvature of Earth's surface, and so by measuring this angle, he related the distance between Alexandria and Syene to the total dimension of the globe.

On the day the Sun shone on the bottom of the wells in Syene, Eratosthenes measured the Sun's position in the sky over Alexandria. It was seven degrees away from the zenith, meaning Syene must be seven degrees away from Alexandria as measured on the circle that is Earth's circumference. Because seven degrees is about one 50th of a full circle (360 degrees), Eratosthenes simply multiplied the distance from Alexandria to Syene -- believed to have been about 515 miles (830 km) -- by 50. He calculated Earth's circumference at 26,000 miles (42,000 km), only five percent away from the modern accepted value of 24,901 miles (40,074 km).

https://stardate.org/astro-guide/faqs/how-was-size-earth-first-measured#:~:text=On the day the Sun,circle that is Earth's circumference.

I would also add that for thousands of years man has been using a sextant to measure the angle of the Sun so they could know their latitude and find themselves on a map of the Earth.

The problem with this (as a proof of ball-Earth) is that the result is similar whether Earth is a sphere or flat. Flat Earthers simply respond that of course the angle of the sun is different at different places, because of trigonometry. To demonstrate this, simply place two upright blocks on a table about 1 meter apart and hold a torch overhead the first upright block. The shadow created by the first block will be almost non-existant, dependent on how well the torch is held overhead, whilst the shadow created by the second block will be more pronounced. This doesn't mean the table is curved - it means trignometry results in different shadows dependent on the position of the blocks and the torch.

(It may have been that Eratosthenes assumed a large sun and a large distance between it and Earth for his "proof". However, these are Heliocentric assumptions, and it's circular reasoning to claim to prove a theory with the very theory one is trying to prove. Flat Earthers typically believe the sun is much smaller and closer than Heliocentrists. This is consistent with observation, which shows the sun's rays approach Earth at different angles, rather than all at the same angle as would be consistent with an [almost] infinitely large sun at an [almost] infinite distance).