I still have my 1943 version of George Mixter's "Primer of Navigation" (which is still available on Amazon.com). When I was a medical
officer on a US Navy
ship in the 60's, Mixter's book was the go to reference for most of the junior line officers trying to learn celestial. This book still resides in the bookcase of my boat CYGNUS. along with HO 211, HO 229 and an updated Nautical Almanac. These became back-ups to navigational calculators which, maintain a complete nautical almanac and reduction tables that do all the "work" for you; I've used Celesticomp for years but this unit has sadly been dead-ended and I must now shell out $400 for a StarPilot.
Of course, I have GPS
(permanent with chart plotter) and a couple of hand-held units. But Celestial Navigation is "fun". I still take sun and twilight star shots just to see how close I get to the GPS
location (usually within a half a mile). And who knows? Someday, somewhere a lightning
strike may fry our electronics
and celestial will get us home!
Sextants are now pretty inexpensive; you can get some for under $400; there are always some on eBay and one can frequently get a quality sextant for even less than $400.