Before everyone rushes out to buy a sextant on EBAY and Bowditches Practical Navigator, take a deep breath.
IF you get one that isn't a cheap brass indian knockoff ( hint, not that many sextants survived from the Titanic)odds are it hasn't been maintained or, and a big or, calibrated and cerified as accurate.
If you want to learn sextant use there are very modest plastic starter units, much like basic compasses for new users.
No, you won't look like Captains Courageous striking a Captain Morgan pose.You also won't loook like a fool with a $600 paperwieght.
And as for it being a dying art, thats like saying a wheelgun is no good in a gunfight. Lots of people still use tested methodologies, not just those making fire with flint and steel.