Alphabetarion # The Sextant

“Until you have the courage to lose sight of the shore, you will not know the terror of being forever lost at sea.” 
 Charles Cook

 Jesse Ramsden, Sextant, 1772                                                           Marsden Hartley. Sextant, 1917

A sextant is a doubly reflecting navigation instrument used to measure the angle between any two visible objects. The principle of the instrument was first implemented around 1730 by John Hadley (1682–1744) and Thomas Godfrey (1704–1749) but it was also found later in the unpublished writings of Isaac Newton (1643–1727).

The primary use of a sextant is to determine the angle between an astronomical object and the horizon for the purposes of celestial navigation. The determination 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 chart.


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