Lighthouse
100 ft tall
Observer 1
15.2 nm away
Sees top only
Observer 2
8 nm away
Sees upper portion
Observer 3
3.0 nm away
Sees full lighthouse
15.2 nm
~8 nm
3.0 nm
100'
6'
Visibility Calculation:
d = 1.22 × (√h₁ + √h₂)
h₁ = observer height (6 ft)
h₂ = object height
Top visible: h₂ = 100 ft → 15.2 nm
Base visible: h₂ = 0 ft → 3.0 nm
Progressive Visibility:
• Beyond 15.2 nm: Lighthouse not visible
• 15.2 nm to 3.0 nm: Partial visibility (top down)
• Within 3.0 nm: Full lighthouse visible
Earth's curvature reveals objects progressively from top to bottom
Lighthouse Visibility Example: 6' Observer Height, 100' Lighthouse
Top Only Zone
Partial Zone
Full Visibility