A sextant
Sisko using an sextant
A sextant was an archaic navigational instrument used aboard ships and some aircraft.
Captain Jean-Luc Picard kept a sextant in his quarters aboard the USS Enterprise-D. (TNG: "The Battle")
When Jono lived in the captain's quarters for some time in 2366, 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")
Background
In the deleted scene from Star Trek Generations, Jean-Luc Picard was given a sextant for Christmas from his family in the Nexus. This scene was included in the special features of the Star Trek Generations Special Edition DVD.
The script of the Star Trek: Deep Space Nine episode "Rapture" called for various "sextant-like instruments" to be positioned in a scene in the holosuite.