Atmospheric Refraction: Why the Horizon Is Not Where You Think
📐 Measuring the Earth
Question
Does the atmosphere bend light enough to hide ships?
Air's index of refraction is ~1.00029 at the ground and falls with altitude, so light bends gradually toward the ground. The crucial detail: the net effect is that objects appear slightly HIGHER than they really are - not lower. Standard refraction at the horizon is ~34 arcminutes (0.57°); at 45° elevation it is ~1 arcminute. Every telescope and survey instrument corrects for it; the flat-earth laser tests fail because they do not model it, and when it is modelled the curvature remains.
The math
Standard refraction: ~34' (0.57°) at the horizon, ~1' at 45° elevation. Surveyors use an effective Earth radius of ~4/3 R: from 100 m eye height the geometric horizon is 35.7 km; with refraction ~41 km - a ~15% extension, not the 'hides the ship' effect that is claimed.
Why it matters
Refraction is real, it is modelled, and it is a fraction of a degree. It cannot account for the dip a $10 clinometer measures, nor for the hulls of the ships at Pensacola. The flat model needs refraction to be many degrees strong - which would make the sky look nothing like it does.