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sextant
A navigational instrument for determining latitude by measuring the angle between some heavenly body and the horizon.

It was invented in 1730 by John Hadley (1682-1744) and can be used only in clear weather. John Hadley was an English mathematician, inventor of the octant (reflecting quadrant) and precursor to the sextant around 1730.

This entry is located in the following unit: Astronomy and related astronomical terms (page 23)