The chronometers at the beginning of the 18th century, several decades after their invention by Huygens, were not very precise, and therefore it was impossible to use only their indications when determining the location of the ship; Only during the 19th century did they fully meet their purpose.
Thus, for half a century, the Moon provides the same assistance as it did thanks to the calculations of Regiomontan Amerigo Vespucci ; She will continue to render this service in those cases when the chronometer refuses to fulfill its purpose or when its testimony will need to be controlled. The moon: research ...
This moon help is that on the basis of the theory of the Lunar movement, which reaches all the great perfection, it is calculated several years in advance for the time intervals following one after another at least three hours later, the place occupied by the center of the Moon disc relative to the bright stars and relatively The sun; These calculations are published in tables, so-called almanacs, or yearbooks.
When this position of the moon is known at the time of observation with an accuracy of a few seconds of the arc, counting not the Greenwich time, then measuring the distance of the moon from the sun or from some other star with the corresponding instrument, the position of which is known at the moment, we can find the Greenwich Time, i.e., the equatorial longitude of the zenith or the Greenwich meridian.
(The local meridian is nothing but a large circle passing through the pole of diurnal rotation and the zenith point in this place). This definition makes it possible to find the geographical longitude of the place of observation, just as it can be achieved with the help of a chronometer, of which we spoke above.
The basis for a more accurate calculation of the positions of the moon in the sky was laid by Newton's works; The task of observers, theoreticians and calculators who lived after him was only to further improve the theory and practice of these calculations. At all times, the Moon had a great influence on the earth. Very often strange things happened on the earth when the moon entered this or that sign of the zodiac (the Moon in Sagittarius, the Moon in Taurus).