A sextant was an archaic navigational instrument used aboard ships and some aircraft.
While stranded on Shuttlepod 1 together in 2151, Malcolm Reed asked Charles Tucker III if he had a sextant handy. Tucker replied that he left it on Enterprise NX-01 with his slide rule. (ENT: "Shuttlepod One")
Captain Jean-Luc Picard kept a sextant in his quarters aboard the USS Enterprise-D. (TNG: "The Battle", "Allegiance", "Captain's Holiday", "Legacy", "Suspicions", "Attached")
When Jono lived in the captain's quarters for some time in 2367, Picard made sure that the boy didn't touch the sextant. (TNG: "Suddenly Human")
Benjamin Sisko used a sextant to navigate while aboard the Bajoran lightship he constructed in late 2371. (DS9: "Explorers")
Tom Paris once complained about 24th century sensors and technology and told Captain Kathryn Janeway that all he needed was a window and a sextant to guide the USS Voyager through space. (VOY: "The Haunting of Deck Twelve")