The horizon is a concept utilized across physics and observational science, marking the apparent visual limit where a large curved body, such as a planet, meets the surrounding atmosphere or sky. From an optical perspective, the perceived location of the horizon is not strictly limited by the geometric curvature alone, but is significantly influenced by atmospheric refraction—the bending of light as it passes through density gradients. This atmospheric effect can cause objects at great distances to appear elevated or displaced from their true position, leading to variations between the observed visual horizon and the calculated theoretical horizon. The study of this limit is essential for accurate surveying, geodesy, and understanding atmospheric optics, as it defines the maximum observable line of sight from a given elevation.