Hemisferium SextantThis Sextant is a reproduction of an Octant of the mid 17th century. By measuring the height of a celestial object such as the stars or the sun, the Octant allows navigators to determine their geographic latitude. A Sextant can also be used to calculate Greenwich Mean Time and as a result geographic longitude by measuring the lunar distance between the moon and another celestial object. In 1731 John Hadley, an English mathematician, and Thomas