The\u00a0horizon\u00a0or\u00a0skyline\u00a0is the apparent line that separates\u00a0earth\u00a0from\u00a0sky, the line that divides all visible directions into two categories: those that intersect the Earth’s surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting intersection of earth and sky is called the\u00a0visible horizon. When looking at a sea from a shore, the part of the sea closest to the horizon is called the\u00a0offing. The word\u00a0horizon\u00a0derives from the\u00a0Greek\u00a0“\u1f41\u03c1\u03af\u03b6\u03c9\u03bd \u03ba\u03cd\u03ba\u03bb\u03bf\u03c2”\u00a0horiz\u014dn kyklos, “separating circle”,from the verb\u00a0\u1f41\u03c1\u03af\u03b6\u03c9\u00a0horiz\u014d, “to divide”, “to separate”, and that from “\u1f45\u03c1\u03bf\u03c2” (oros), “boundary, landmark”.<\/p>\n
Historically, the distance to the visible horizon has long been vital to survival and successful navigation, especially at sea, because it determined an observer’s maximum range of vision and thus of\u00a0communication, with all the obvious consequences for safety and the transmission of information that this range implied. This importance lessened with the development of the\u00a0radio\u00a0and the\u00a0telegraph, but even today, when flying an\u00a0aircraft\u00a0under\u00a0visual flight rules, a technique called\u00a0attitude flying\u00a0is used to control the aircraft, where the pilot uses the visual relationship between the aircraft’s nose and the horizon to control the aircraft. A pilot can also retain his or her\u00a0spatial orientation\u00a0by referring to the horizon.<\/p>\n
In many contexts, especially\u00a0perspective\u00a0drawing, the curvature of the\u00a0Earth\u00a0is disregarded and the horizon is considered the theoretical line to which points on any\u00a0horizontal plane\u00a0converge (when projected onto the picture plane) as their distance from the observer increases. For observers near\u00a0sea level\u00a0the difference between this\u00a0geometrical horizon\u00a0(which assumes a perfectly flat, infinite ground plane) and the\u00a0true horizon\u00a0(which assumes a\u00a0spherical Earth\u00a0surface) is imperceptible to the naked eye dubious\u00a0\u2013\u00a0discuss but for someone on a 1000-meter hill looking out to sea the true horizon will be about a degree below a horizontal line.<\/p>\n","protected":false},"excerpt":{"rendered":"
The\u00a0horizon\u00a0or\u00a0skyline\u00a0is the apparent line that separates\u00a0earth\u00a0from\u00a0sky, the line that divides all visible directions into two categories: those that intersect the Earth’s surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting intersection of earth and sky is called the\u00a0visible horizon. When looking at …<\/p>\n