What is Horizon?
[[File:Horizon.jpg|thumb|right|Horizon.]] [[File:Earth's horizon as seen from Shuttle Endeavour.jpg|thumb|right|View of Earth's horizon as seen from [[Space Shuttle Endeavour|Space Shuttle ''Endeavour'']], 2002.]] 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''. == Other websites == * [http://newton.ex.ac.uk/people/sque/physics/horizon/ Derivation of the distance to the horizon] {{science-stub}} [[Category:Astronomical phenomena]]