How is the circumference of the earth calculated?
From visible horizon.
From visible horizon:
Let h be the height of the flag mast of a ship, from sea level. If d is
the maximum sea-level distance from which the top could be seen.
the circumference of the Earth is nearly
If h = 20 meters = 0.02 km and d = 11288 meters,
the radius of the Earth
d=(radius)(angle subtended at the center, in radian)=
Here the proportion
If T is the Top of flag mast, O is the observer, C is the center of the
as h/R is very small.
So, the approximation formula is