Nocturnal Quadrant

This rare combination of nocturnal and quadrant was used by astronomers to make accurate observations of the heavens for star charts and astrological forecasts. For mariners the instrument was used to determine latitude. The quadrant side of this instrument contains two sights used for sighting Polaris and a degree scale for reading the latitude. Readings were taken from Polaris and adjustments made with calibration tables for errors caused by movement of the star around True North. The instrument is stamped "QUADRANS HORARIUM ADLATIT CRAWD XLIII MXL," suggesting that it was to be used hourly at latitude 43 degrees.

Before the invention of the chronometer in the eighteenth century, mariners used the nocturnal to tell time at night from the positions of Polaris and its orbiting guard star Kochab.

For more information, e-mail collections@MarinersMuseum.org.