Sextant

sextant [ SEK-stuh'nt ]
[ noun ]

MEANING :
1. an instrument used to determine latitude and longitude at sea by measuring the altitudes of the stars or other celestial bodies

USAGE EXAMPLE 1 :
In the old days, before the discovery of radar the sextant was used in the navigation of ships.

USAGE EXAMPLE 2 :
Last week, a sextant -- an instrument used by navigators to measure the angular distance of the sun from the horizon -- with the inscription "Mercier" was found near "the fault".