Horizon
The horizon (from Greek orizein, to limit) is the line that separates earth from sky. But at many places the true horizon cannot be seen as there are trees, buildings, mountains and so forth. The line is then called visible horizon.
Horizon Media
True, visible, and astronomical horizons. Not shown: refracted horizon.
The curvature of the horizon as observed from a Space Shuttle at an altitude of 226 km (140 mi).
Bird's-eye view created with a horizon line above the subject of the scene (in this case, Paris in 1850).
A sequence of pictures taken at Strait of Magellan, Chile, showing a tanker ship sailing towards the camera and rising over the horizon, demonstrating the Earth's curvature. Distance at first picture is about 18 km which would imply a theoretical horizon vertical drop of about 23 meters. Ship length is 186 m.
Geometrical distance to the horizon, Pythagorean theorem
Maximum zenith angle for elevated observer in homogeneous spherical atmosphere
Geometrical horizon distance
A ship moving away, beyond the horizon
Two points on the horizon are at the intersections of the lines extending the segments representing the edges of the building in the foreground. The horizon line coincides here with the line at the top of the doors and windows.
