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==Origin==
New Latin ''sextant''-, ''sextans'' sixth part of a [[circle]], from [[Latin]], sixth part, from ''sextus'' sixth
*[http://en.wikipedia.org/wiki/17th_century 1628]
The scale of a sextant has a length of ⅙ of a turn (60°); hence the sextant's name (sextāns, -antis is the Latin word for "one sixth"). An [https://en.wikipedia.org/wiki/Octant_(instrument) octant] is a similar device with a shorter scale (⅛ turn, or 45°), where as a quintant (⅕ turn, or 72°) and a quadrant (¼ turn, or 90°) have longer scales.
Sir [https://en.wikipedia.org/wiki/Isaac_Newton Isaac Newton] (1643–1727) invented the principle of the doubly reflecting navigation instrument (a reflecting quadrant—see Octant (instrument)), but never published it. Two men independently developed the octant around 1730: [https://en.wikipedia.org/wiki/John_Hadley John Hadley] (1682–1744), an English mathematician, and [https://en.wikipedia.org/wiki/Thomas_Godfrey_(inventor) Thomas Godfrey] (1704–1749), a glazier in Philadelphia. [https://en.wikipedia.org/wiki/John_Bird_(astronomer) John Bird] made the first sextant in 1757. The octant and later the sextant, replaced the Davis quadrant as the main instrument for [[navigation]].
==Definition==
*1: an instrument for [[measuring]] [[angular]] distances used especially in [[navigation]] to observe altitudes of celestial bodies (as in ascertaining latitude and longitude)
==Description==
A '''sextant''' is an instrument used to [[measure]] the [[angle]] between any two visible objects. Its primary use is to determine the angle between a [[celestial]] object and the [[horizon]] which is known as the object's altitude. Using this measurement is known as ''sighting the object'', shooting the object, or taking a sight and it is an essential part of [https://en.wikipedia.org/wiki/Celestial_navigation celestial navigation]. The angle, and the time when it was measured, can be used to [[calculate]] a position line on a nautical or aeronautical chart. Common uses of the sextant include sighting the [[sun]] at solar noon and sighting [https://en.wikipedia.org/wiki/Polaris Polaris] at night (in the Northern Hemisphere), to find one's latitude. Sighting the height of a landmark can give a measure of distance off and, held horizontally, a sextant can measure angles between objects for a position on a chart. A sextant can also be used to measure the [https://en.wikipedia.org/wiki/Lunar_distance_(navigation) lunar distance] between the [[moon]] and another celestial object (e.g., [[star]], [[planet]]) in order to determine [https://en.wikipedia.org/wiki/Greenwich_time Greenwich time] which is important because it can then be used to determine the longitude.[https://en.wikipedia.org/wiki/Sextant]
[[Category: Astronomy]]
==Origin==
New Latin ''sextant''-, ''sextans'' sixth part of a [[circle]], from [[Latin]], sixth part, from ''sextus'' sixth
*[http://en.wikipedia.org/wiki/17th_century 1628]
The scale of a sextant has a length of ⅙ of a turn (60°); hence the sextant's name (sextāns, -antis is the Latin word for "one sixth"). An [https://en.wikipedia.org/wiki/Octant_(instrument) octant] is a similar device with a shorter scale (⅛ turn, or 45°), where as a quintant (⅕ turn, or 72°) and a quadrant (¼ turn, or 90°) have longer scales.
Sir [https://en.wikipedia.org/wiki/Isaac_Newton Isaac Newton] (1643–1727) invented the principle of the doubly reflecting navigation instrument (a reflecting quadrant—see Octant (instrument)), but never published it. Two men independently developed the octant around 1730: [https://en.wikipedia.org/wiki/John_Hadley John Hadley] (1682–1744), an English mathematician, and [https://en.wikipedia.org/wiki/Thomas_Godfrey_(inventor) Thomas Godfrey] (1704–1749), a glazier in Philadelphia. [https://en.wikipedia.org/wiki/John_Bird_(astronomer) John Bird] made the first sextant in 1757. The octant and later the sextant, replaced the Davis quadrant as the main instrument for [[navigation]].
==Definition==
*1: an instrument for [[measuring]] [[angular]] distances used especially in [[navigation]] to observe altitudes of celestial bodies (as in ascertaining latitude and longitude)
==Description==
A '''sextant''' is an instrument used to [[measure]] the [[angle]] between any two visible objects. Its primary use is to determine the angle between a [[celestial]] object and the [[horizon]] which is known as the object's altitude. Using this measurement is known as ''sighting the object'', shooting the object, or taking a sight and it is an essential part of [https://en.wikipedia.org/wiki/Celestial_navigation celestial navigation]. The angle, and the time when it was measured, can be used to [[calculate]] a position line on a nautical or aeronautical chart. Common uses of the sextant include sighting the [[sun]] at solar noon and sighting [https://en.wikipedia.org/wiki/Polaris Polaris] at night (in the Northern Hemisphere), to find one's latitude. Sighting the height of a landmark can give a measure of distance off and, held horizontally, a sextant can measure angles between objects for a position on a chart. A sextant can also be used to measure the [https://en.wikipedia.org/wiki/Lunar_distance_(navigation) lunar distance] between the [[moon]] and another celestial object (e.g., [[star]], [[planet]]) in order to determine [https://en.wikipedia.org/wiki/Greenwich_time Greenwich time] which is important because it can then be used to determine the longitude.[https://en.wikipedia.org/wiki/Sextant]
[[Category: Astronomy]]
