horyzontu

Horizon, in its broad sense, is the apparent boundary between the sky and the surface of the Earth or sea as seen from a given location. It is an optical rather than a fixed line, shaped by the curvature of the Earth, the observer’s height, and atmospheric conditions.

There are several related concepts. The geometric or true horizon is the circle on the Earth's surface where the tangent plane at the observer’s location meets the ground. The visible horizon is what a observer actually perceives, which may be hidden or altered by terrain, bodies of water, or atmospheric effects. The astronomical horizon is the reference plane used in celestial coordinate systems, defined as the intersection of the observer’s local vertical with the celestial sphere.

Distance to the horizon depends on height. A common approximation is d ≈ sqrt(2Rh), where R is Earth’s radius (about 6,371 km) and h is the observer’s elevation above sea level. For a person standing at roughly 1.7 meters, the horizon is about 4.7 kilometers away. Atmospheric refraction can lift the apparent horizon slightly, and surface conditions such as waves or haze can affect visibility.

Historically and culturally, the horizon has served as a practical guide in navigation and exploration and as a metaphor for limits and possibilities. Etymologically, the word derives from Greek horizōn, meaning boundary, and entered European languages via Latin and French. In Polish, the genitive form is horyzontu, used in phrases describing edges or limits of the horizon.