BTW A Sextant calculates from a horizon.
it. Why?
Because at sea the horizon is the best reference available for
calculating the local horizontal.
And if the observer is close to sea-level the horizon is very close to the local horizontal The horizon falls below the local horizontal (eye-level) by an amount dependent on observer height.
And any sailor or navigator knows that a correction must be applied to allow for this
dip angle. Just look up any
Naval Almanac from as far back as you like up to the present day!
A word in the English language derived from horizontal not a curved geometrical line.
That is total fiction perpetuated by flat earthers ignorant of their own language. Please read:
horizon (n.)
late 14c., orisoun, from Old French orizon (14c., Modern French horizon), earlier orizonte (13c.), from Latin horizontem (nominative horizon), from Greek horizon (kyklos) "bounding (circle)," from horizein "bound, limit, divide, separate," from horos "boundary, landmark, marking stones."
Put simply the word
horizon is means the "bounding (circle)" between the sky and the earth and has nothing to do with its being straight - even though it almost is!
A Sextant for a spherical world is actually foreign to you.
No, a sextant was developed for an earth known to be spherical and from very early days it was known that a "dip angle correction" that depended on the observer elevation above sea-level.
You let me know when you have actually taken a real picture of a curvizon. Just 1 would help, but you can't do it. Why?
In case you didn't know the ocean horizon on the Globe is almost perfectly straight and that is exactly as it should be.
If it were curved it could mean that we lived on a small spherical object or a larger cylinder.