Painting of sextant use by Winslow Homer, 'Eight Bells', 1886. A Sextant is a device used on a ship or aircraft for measuring angles, such as those between stars or that between the sun and the earth, in order to discover the exact position of the ship or aircraft. The sextant is an instrument for measuring the angular distance between celestial objects, and resembles an octant, the development of an older instrument called a Falstaff which measured the angle of the sun from the length of its shadow but that was always a bit tricky at sea. A sowester is a waterproof hat with wide slanting brim longer in back than in front