'All this starlore stuff is running around her captains head and he reckons he might try steering our little ship by the stars on his watch. He selects a group of stars close to her masthead, and that he can recognise easily. Studying his star chart, it turns out to be the planet Jupiter, with some other stars in the background, forming a pattern that he can identify instantly. The warm night breeze is well round on her port quarter, and she is gambolling along at an easy eight plus knots. As the increments of time increase, her captain gains more confidence. Jupiter and companions remain utterly unmoved all this time and beam down their twinkling radiance benevolently on our little ship, and her now somewhat more comfortable captain. He is enjoying himself now and taking in more of his surroundings, as opposed to fixating his eye permanently on his sky guide. After an hour he is quite relaxed, hand lightly on the wheel, and glancing upward only occasionally, to check that Jupiter and company have not run away! Over a four hour watch, travelling at eight knots or so, she will have moved westward not more than half of one degree, i.e. thirty nautical miles, so any change of her position in relation to the stars would be so infinitesimally small, there would be no visible variance.