Debunking Flat Earth Misconceptions
An astrolabe is a device historically used to determine the date and time of day from the positions of the sun or stars. Astrolabe was used from classical antiquity, about the 2nd century BC, until the age of discovery. It was superseded by the more accurate sextant, star charts, and time-keeping devices.
Flat-Earthers claim an astrolabe can work because Earth is flat. In reality, astrolabes are designed using the spherical Earth model. They could not possibly work if Earth is flat.
We can determine if a star is visible from a specific location using the declination of the star and the latitude of the observer, subject to other conditions like observer’s topology, the magnitude of the star, weather conditions, etc. It is possible to do this because Earth is a rotating sphere.
If the Earth is flat, every star would have been visible all night from every location. We don’t see the same stars every night because some of them are below the horizon and obscured by the Earth.