sextant

American  

[sek-stuhnt] / ˈsɛk stənt /

noun

1. an astronomical instrument used to determine latitude and longitude at sea by measuring angular distances, especially the altitudes of sun, moon, and stars.

2. Astronomy. Sextant, the constellation Sextans.

---

sextant British  

/ ˈsɛkstənt /

noun

1. an optical instrument used in navigation and consisting of a telescope through which a sighting of a heavenly body is taken, with protractors for determining its angular distance above the horizon or from another heavenly body

2. a sixth part of a circle having an arc which subtends an angle of 60°

---

sextant Scientific  

/ sĕk′stənt /

1. An instrument containing a graduated 60° arc and a movable pivoted arm corresponding to the radius of the arc's circle, used in celestial navigation to measure the altitude of a celestial body in order to determine the observer's latitude and longitude. A horizontally mounted telescope and two small mirrors are arranged so that the observer can, by moving the pivoted arm, sight the horizon and the reflected image of the celestial body in the same line, giving a reading along the arc that is used to look up the observer's position in a published table.

---

Etymology

Origin of sextant

First recorded in 1590–1600; from Latin sextant- (stem of sextāns ) sixth part of a unit; see sext ¹, -ant

Explanation

A sextant is a tool for measuring the angles between heavenly bodies — the kind found in outer space. Used as a navigational tool out at sea, it helps determine a ship's longitude and latitude. There is nothing sexy about a sextant, unless you're a sailor. Even then, in today's world of sophisticated instrumentation, it's considered quaint and old-fashioned. The noun sextant dates back to the late 16th century, from the Latin word sextans, meaning "sixth part." The sextant uses a graduated arc of 60° (there's the six reference) for measuring the altitude of the planets and stars.

Example Sentences

As navigator, Lovell took with him a sextant to take star readings - in case the computers failed and they had to find their own way home.

From BBC • Aug. 8, 2025

Fun as it is to watch Anne fiddle with his sextant, you almost prefer her scenes with her dreamy/scheme-y cousin, Mr. Elliot, who in this retelling is bracingly straightforward about his financial motives.

From Los Angeles Times • Jul. 13, 2022

The next morning, after 16 hours of flying with only a compass and sextant for direction, the pair spotted land.

From Washington Post • May 21, 2022

Albert Read stood in the nose of the NC-4 fuselage for the 15-hour flight, taking readings with his sextant when he could, returning to a small desk below to make calculations.

From Washington Times • May 16, 2019

Then one evening during the dog watch, before the stars were visible, Nat leveled his sextant to catch the horizon.

From "Carry On, Mr. Bowditch" by Jean Lee Latham