Editing Sextant (section)

{{Short description|Tool for angle measurement}}
{{About|the sextant as used for navigation}}
{{Confuse|Sexton (disambiguation)}}
{{refimprove|date=March 2024}}
[[File:Sextant.jpg|thumb|A sextant]]

A '''sextant''' is a [[reflecting instrument|doubly reflecting navigation instrument]] that measures the [[angular distance]] between two visible objects. The primary use of a sextant is to measure the angle between an [[astronomical object]] and the [[horizon]] for the purposes of [[celestial navigation]].

The estimation of this angle, the altitude, is known as ''sighting'' or ''shooting'' the object, or ''taking a sight''. The angle, and the time when it was measured, can be used to calculate a [[position line]] on a nautical or aeronautical [[nautical chart|chart]]—for example, sighting the [[Sun]] at [[solar noon|noon]] or [[Polaris]] at night (in the Northern Hemisphere) to estimate [[latitude]] (with [[sight reduction]]). 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 [[fix (position)|position on a chart]].<ref>{{cite journal |last=Seddon |first=J. Carl |title=Line of Position from a Horizontal Angle |journal=Journal of Navigation |date=June 1968 |volume=21 |issue=3 |pages=367–369 |doi=10.1017/S0373463300024838 |issn=1469-7785 |doi-access=free |bibcode=1968JNav...21..367S }}</ref> A sextant can also be used to measure the [[lunar distance (navigation)|lunar distance]] between the moon and another celestial object (such as a star or planet) in order to determine [[Greenwich Mean Time]] and hence [[longitude]].

The principle of the instrument was first implemented  around 1731 by [[John Hadley]] (1682–1744) and [[Thomas Godfrey (inventor)|Thomas Godfrey]] (1704–1749), but it was also found later in the unpublished writings of [[Isaac Newton]] (1643–1727).<ref>{{cite book |last=Brodetsky |first=S. |url=https://books.google.com/books?id=uCczEQAAQBAJ&pg=PA135 |title=Sir Isaac Newton: A Brief Account of His Life and Work |date=2024 |publisher=Taylor & Francis Group |isbn=978-1-032-94129-5 |edition=1st |series=Routledge Revivals Series |location=Oxford |pages=135}}</ref>

In 1922, it was modified for aeronautical navigation by Portuguese navigator and naval officer {{lang|pt|[[Carlos Viegas Gago Coutinho|Gago Coutinho]]|italic=no}}.