|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°|
|[C17: from Latin sextāns one sixth of a unit]|
|sextant (sěk'stənt) Pronunciation Key
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.