For other uses of horizon, see Horizon , 2002.]]The horizon (Ancient Greek ? ??????, /ho horídzôn/, from ???????, "to limit") is the apparent line that separates earth from sky. More precisely, it is the line that divides all of the directions one can possibly look into two categories: those which intersect the Earth's surface, and those which do not. At many locations, the true horizon is obscured by nearby trees, buildings, mountains and so forth. The resulting intersection of earth and sky is instead described as the visible horizon. Appearance and usage For observers aboard a ship at sea, the true horizon is strikingly apparent. Historically, the distance to the visible horizon has been extremely important as it represented the maximum range of communication and vision before the development of the radio and the telegraph. Even today, when flying an airc

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