The visibility of distant objects is limited by the transparency of the atmosphere (absorption and scattering of light) and the curvature of the earth’s surface. Even if atmospheric visibility is excellent, objects located far away may not be visible because they are beyond the true horizon.
The calculator below determines:
- the approximate distance at which the top of an object can be seen with good atmospheric visibility (d2)
- the approximate distance to the true horizon (d1).
The height of the observer’s eyes above the ground (h1) and the height of the object located beyond the horizon (h2) must be entered into the calculator, as shown in the figure below.
Notes:
- The calculator uses the average refractive index (0.14). After selecting the “Refractive index other than average” button, you can perform calculations for a different value of this index.
- The calculator assumes a smooth earth’s surface. Naturally, hills, buildings or forests may obscure objects that would be visible without them.
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update: August 2024