Technical Disclaimer
Important parameters and geodetic limitations regarding Earth curvature models.
1. Spherical Earth Model Approximation
Calculations provided by HorizonCalc are based on a perfectly spherical Earth model using a mean volumetric radius ($R$) of 6,371 kilometers (3,958.8 miles).
In reality, the Earth is an oblate spheroid (flattened slightly at the poles), and its shape is officially represented by ellipsoidal reference ellipsoids like WGS84 or GRS80. For regional calculations (under a few hundred miles), the spherical approximation is highly accurate, introducing errors of less than 0.1%. However, it does not account for local topography, elevation fluctuations, or sea-level variations (geoid height differences).
2. Variability of Atmospheric Refraction
Standard atmospheric refraction models ($7/6 \cdot R$, or a refraction coefficient $k = 0.17$) represent typical atmospheric conditions under standard temperature and pressure.
However, real-world atmospheric refraction is highly dynamic and changes constantly based on local temperature gradients, humidity levels, air pressure, and altitude. Extreme weather conditions (such as cold air over warm water or vice versa) can cause significant deviations, making objects appear much higher (looming) or completely disappearing (sinking) relative to standard calculations. These calculations should be used as a theoretical guide, not an absolute guarantee of optical visibility.
3. Educational and Informative Scope
The outputs, calculations, dynamic diagrams, and graphs provided by this site are designed for educational, analysis, and research reference.
Under no circumstances should the calculations on this site be used for navigation, safety-critical aerospace engineering, maritime route planning, or commercial surveying where life, property, or legal precision is at stake.
Always consult licensed professional land surveyors, oceanographers, or specialized geodetic engineers for certified geographic measurements.