NavList:

Perhaps the best proof that celestial navigation is not an "art" is that it can be learned from a book and in a fairly short period of time. It requires no "personal genius" or insight or intuition and no lifelong devotion to become sufficiently skilled in it to cross an ocean. It can even be learned as a rote task, very much like following a cookbook recipe. Indeed, that is exactly why it was so hugely successful. Celestial navigation did not depend on years of study under a master tutor. This distinguishes it from most of the more ancient traditions of navigation which could very well be counted as "arts".

The proof that celestial navigation is not a science is simpler. Sciences discover new knowledge. The practitioners of "nautical astronomy" could be counted as scientists at a rather basic level since they try to develop new methods of navigating by the stars. But navigators taking sights and working celestial navigation problems are definitely not doing science. What they are doing is "scientific" in that they use technical tools and methods, but it is a fixed systematic set of rules (unless a navigator chooses to expand his or her skills, either out of personal interest or a desire for professional advancement). In this sense, it very closely resembles the disciplines of engineering.