<Dd> cos ⁡ ψ = R E μ 0 (R E + h) μ, (\ displaystyle \ cos \ psi = (\ frac ((R) _ (\ text (E)) (\ mu) _ (0)) (\ left (((R) _ (\ text (E))) + h \ right) \ mu)) \,,) </Dd> <P> where h is the observer's height above the Earth, μ is the index of refraction of air at the observer's height, and μ is the index of refraction of air at Earth's surface . </P> <P> The refraction must be found by integration of </P> <Dl> <Dd> δ = − ∫ 0 h tan ⁡ φ d μ μ, (\ displaystyle \ delta = - \ int _ (0) ^ (h) (\ tan \ phi (\ frac ((\ text (d)) \ mu) (\ mu))) \,,) </Dd> </Dl>

How far can you see before the curvature of the earth