If the celestials were physical then the altitude angle to them would change with the observer’s height above sea level.

Flat Earther ignorance knows no bounds and is often wilful. To them, stars and planets are just “lights in the sky”. Any suggestion that a great deal is known about celestial objects is met with denial; because we cannot touch them, they believe we can know nothing about them. Astronomy, cosmology and the exploration of space are all a big lie to them.

The obvious answer to the above is that celestial objects are generally too far away to exhibit measurable parallax by changing position on the Earth. The Moon, by the way, does and has to be accounted for in celestial navigation. The Sun also exhibits a small but measurable parallax across the surface of the Earth.