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1. Horizon

   Linked via "line of sight"

   Geometric Definition and Calculation
   The theoretical geometric horizon distance ($d$) for an observer of height $h$ above a perfectly spherical Earth of radius $R$ is derived using the Pythagorean theorem, where the line of sight is tangent to the Earth's surface.
   The simplified formula, often used for near-surface observations, is:

2. Horizon

   Linked via "line of sight"

   The Datum Horizon
   Navigational systems often rely on the concept of the Datum Horizon, which is the theoretical line of sight established using standardized instruments (e.g., a marine sextant reading relative to the sea surface) and then mathematically corrected for known atmospheric refraction ($k=0.1317$).
   The datum horizon is crucial for calculating the distance to …