NavList:

Alexandre wrote

I learned Cel Nav from books, long before I saw a real sextant for the first time.
Good books are abundant, and many of them can be obtained for free.

I studied various navigation texts (purchased from second hand bookshops) for forty years while my sextant (which I had purchased from an Ancient Mariner) was packed away. About six months ago I joined this forum and decided to practice navigation using an artificial horizon. It was a difficult learning curve but with the assistance of this forum I succeeded. I can now take sights and and confirm that GPS is correct to a nm or so (-;

How you go about learning will depend on why you want to learn. In my case I am an armchair navigator interested in the many reduction methods used over the centuries. Therefore I am interested in meridian altitudes, long by chron, intercepts, lunars, equal altitudes, short methods, longhand methods, mathematical tables, Bowditch, Squire Lecky   etc  etc   etc.

On the other hand if you are a practical navigator you probably only need to  know about intercepts and 229 (or is it 249?).

The point I am making is that astro is a very broad subject and you can learn as much or as little as you want. I recomment browsing the archives of this forum and if you do not find the answers you want then ask!