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==Origin==
[http://nordan.daynal.org/wiki/index.php?title=English#ca._1100-1500_.09THE_MIDDLE_ENGLISH_PERIOD Middle English] ''cenyth'', ''senyth'', from Middle French ''cenit'', from Medieval Latin, from Old Spanish ''zenit'', ''modification'' of Arabic ''samt'' (''al-ra's'') way (over one's head)
*[http://en.wikipedia.org/wiki/14th_century 14th Century]
The word "zenith" derives from the inaccurate [[reading]] of the Arabic expression سمت الرأس (samt ar-ra's), meaning "[[direction]] of the head" or "[[path]] above the head", by Medieval Latin scribes in the [http://en.wikipedia.org/wiki/Middle_Ages Middle Ages] (during the 14th century), possibly through Old Spanish. It was reduced to 'samt' ("[[direction]]") and miswritten as 'senit'/'cenit', as the "m" was misread as an "ni". Through the Old French 'cenith', 'zenith' first appeared in the 17th century.
==Definitions==
*1: the point of the [http://en.wikipedia.org/wiki/Celestial_sphere celestial sphere] that is directly opposite the [http://en.wikipedia.org/wiki/Nadir nadir] and vertically above the [[observer]] — see [http://en.wikipedia.org/wiki/Azimuth azimuth] illustration
*2: the highest [[point]] reached in the heavens by a celestial body
*3: [[culminating]] [[point]] : [[acme]] <at the zenith of his powers — John Buchan>
==Description==
The '''zenith''' is an [[imaginary]] point directly "above" a particular location, on the imaginary [http://en.wikipedia.org/wiki/Celestial_sphere celestial sphere]. "Above" means in the [[vertical]] direction opposite to the apparent [[gravitational]] force at that location. The opposite direction, i.e. the direction in which gravity pulls, is toward the [http://en.wikipedia.org/wiki/Nadir nadir].
The term ''zenith'' is sometimes used to refer to the highest [[point]] reached by a celestial body during its apparent [[orbit]] around a given point of [[observation]]. This sense of the word is often used to [[describe]] the location of the [[Sun]] ("The sun reached its zenith..."), but to an [[astronomer]] the sun doesn't have its own zenith, and is at the zenith only if it is directly overhead.
In a scientific [[context]], the zenith is the direction of [[reference]] for measuring the zenith angle, the angle between a direction of interest (e.g., a star) and the local zenith.
In [[astronomy]], the altitude in the [http://en.wikipedia.org/wiki/Horizontal_coordinate_system horizontal coordinate system] and the zenith angle are [[complementary]] [[angles]], with the [[horizon]] perpendicular to the zenith. The astronomical [http://en.wikipedia.org/wiki/Meridian_(astronomy) meridian] is also determined by the zenith, and is defined as a circle on the celestial sphere that passes through the zenith, nadir, and the [http://en.wikipedia.org/wiki/Celestial_pole celestial poles].
Zenith is also used to determine the time of Dhuhr (midday) prayer by Muslims which is when the sun passes the zenith.
[[Category: Astronomy]]
==Origin==
[http://nordan.daynal.org/wiki/index.php?title=English#ca._1100-1500_.09THE_MIDDLE_ENGLISH_PERIOD Middle English] ''cenyth'', ''senyth'', from Middle French ''cenit'', from Medieval Latin, from Old Spanish ''zenit'', ''modification'' of Arabic ''samt'' (''al-ra's'') way (over one's head)
*[http://en.wikipedia.org/wiki/14th_century 14th Century]
The word "zenith" derives from the inaccurate [[reading]] of the Arabic expression سمت الرأس (samt ar-ra's), meaning "[[direction]] of the head" or "[[path]] above the head", by Medieval Latin scribes in the [http://en.wikipedia.org/wiki/Middle_Ages Middle Ages] (during the 14th century), possibly through Old Spanish. It was reduced to 'samt' ("[[direction]]") and miswritten as 'senit'/'cenit', as the "m" was misread as an "ni". Through the Old French 'cenith', 'zenith' first appeared in the 17th century.
==Definitions==
*1: the point of the [http://en.wikipedia.org/wiki/Celestial_sphere celestial sphere] that is directly opposite the [http://en.wikipedia.org/wiki/Nadir nadir] and vertically above the [[observer]] — see [http://en.wikipedia.org/wiki/Azimuth azimuth] illustration
*2: the highest [[point]] reached in the heavens by a celestial body
*3: [[culminating]] [[point]] : [[acme]] <at the zenith of his powers — John Buchan>
==Description==
The '''zenith''' is an [[imaginary]] point directly "above" a particular location, on the imaginary [http://en.wikipedia.org/wiki/Celestial_sphere celestial sphere]. "Above" means in the [[vertical]] direction opposite to the apparent [[gravitational]] force at that location. The opposite direction, i.e. the direction in which gravity pulls, is toward the [http://en.wikipedia.org/wiki/Nadir nadir].
The term ''zenith'' is sometimes used to refer to the highest [[point]] reached by a celestial body during its apparent [[orbit]] around a given point of [[observation]]. This sense of the word is often used to [[describe]] the location of the [[Sun]] ("The sun reached its zenith..."), but to an [[astronomer]] the sun doesn't have its own zenith, and is at the zenith only if it is directly overhead.
In a scientific [[context]], the zenith is the direction of [[reference]] for measuring the zenith angle, the angle between a direction of interest (e.g., a star) and the local zenith.
In [[astronomy]], the altitude in the [http://en.wikipedia.org/wiki/Horizontal_coordinate_system horizontal coordinate system] and the zenith angle are [[complementary]] [[angles]], with the [[horizon]] perpendicular to the zenith. The astronomical [http://en.wikipedia.org/wiki/Meridian_(astronomy) meridian] is also determined by the zenith, and is defined as a circle on the celestial sphere that passes through the zenith, nadir, and the [http://en.wikipedia.org/wiki/Celestial_pole celestial poles].
Zenith is also used to determine the time of Dhuhr (midday) prayer by Muslims which is when the sun passes the zenith.
[[Category: Astronomy]]
