# Flat vs curved Earth horizon?

We consider the Earth is a spheroid and that the horizon is an intersection of the sky and Earth. From this we can conclude that the horizon is always flat, because it's a circle. This explains why we observe a flat horizon, given the geometrical properties described.

My question is, when we get pretty high in altitude over 10.6km, why can we start to see a curved horizon? Please correct me if the first assumptions are wrong as well.

• I smell flat earth... If this is indeed the case believe me: curvature of the horizon is the least of your problem. You should focus on statistics.. Dec 14, 2020 at 11:06
• The horizon seems flat from the point of view of an observer who is very close to the surface (relative to the radius of the Earth). Dec 14, 2020 at 14:25
• @Noumeno No, I'm just trying to figure out why the horizon curves as I was under the impression that since the horizon is a circle it would always look flat regardless of how high we were. If the Earth was flat, the concept of a horizon would likely not even exist. Dec 14, 2020 at 17:13