Sentence:  With cheap quartz watches (several, for reliability) we can do all the modern celestial navigation we could want. But learning and practicing <WSD>lunars</WSD> gives us deeper insight into celestial navigation; an appreciation for their historical importance and difficulty; and perhaps most significant of all, after conquering <WSD>lunars</WSD> we can appreciate the great convenience of St. Hilaire sights and modern quartz watches. Moreover, in the rare event of losing UT, with <WSD>lunars</WSD> and only a poor watch we can still be confident of finding our longitude at sea (well, OK, to within 30′). 
Meaning of the word marked with <WSD> tags:  An observation of a (angle between the Moon and another celestial body), especially for establishing the longitude of a ship at sea.