Quadrant (instrument)

A quadrant is an instrument used to measure angles up to ninety degrees, applied historically to astronomy and navigation for tasks including finding longitude, latitude and the time of day. Its history reaches back to at least the Rigvedic period in India, around 1500 to 1000 BC, when instruments called tureeyams were used to measure solar eclipses, and the astronomer Ptolemy described a version around AD 150 that measured the height of the noon sun by tracking the shadow a peg cast on a graduated ninety degree arc. Medieval Islamic astronomers refined the design further, developing four distinct types of quadrant used in observatories across the Middle East, and in the thirteenth century the Jewish astronomer Jacob ben Machir ibn Tibbon created the novus quadrans, notable as the first quadrant built without several moving parts. As instruments became smaller and easier to carry, the quadrant found wide use at sea, with the navigator Diogo Gomes recorded as the first to use one for maritime navigation in 1461, and Edmund Gunter's 1618 pocket sized version, marked with projections of the tropics, the equator, the horizon and the ecliptic, made it possible to work out time and date calculations while at sea.