From a beach you see about 5 km; from a summit, hundreds. Enter your eye height, the height of a distant subject (a peak, a lighthouse, a skyline) and its distance to see whether it's visible and how much is hidden below the horizon.
Includes standard atmospheric refraction.
How it works
Horizon ≈ 3.86·√h km (h in m, with refraction). Hidden height ≈ ((d − 3.86√h₁) ÷ 3.86)² m.
FAQ
Why use refraction?
The atmosphere bends light slightly downward, so you see a little farther than geometry alone suggests.
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