Sextant

A navigation instrument used by sailors and sometimes pilots. 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 chart.

The frame of a sextant is in the shape of a sector which is approximately  1⁄6 of a circle (60°).