Romantically, we sailors love to say that in the night we talk with the stars, they listen to us and respond. We ask them to show us the way to back home, or if they can tell us where we are when the ship is in the nowhere of the immense ocean, other times we simply share thoughts and secrets, homesickness or a love that we cradle in our hearts. The stars always respond, punctually indicating the route to follow. This is a sort of bond almost as old as humanity. The most fascinating thing about astronomical navigation is that fantasy mixes with reality, in a literal sense. Basically on Earth to orient ourselves we use only one system, that of geographical coordinates, using the North and South Pole, the East and West cardinal points, the Equator and the Greenwich Meridian as reference points. With these references, through latitude and longitude we find any position, whether it is ours or that of the destination. With astronomical navigation, however, we can use four systems, two that refer to the observer called “Hourly local coordinate system and Altazimuth local coordinate system”, and two “Uranographic” systems, Equatorial Uranographic and Ecliptic Uranographic. The celestial bodies, whether planets or stars, each have their own distance, their own height, etc. Furthermore, the universe is immense, threedimensionality must be taken into account, and that certain stars have very large distances. With a bit of cunning and pure imagination we invented the “Celestial Sphere”, which when drawn on a plane becomes “a circle around the Earth”, and it is pretended that all the stars rest on this Sphere. By “stretching” the terrestrial references they are expanded to the Celestial Sphere, the North Pole becomes the “North Celestial Pole” (PNc), the South Pole becomes the “South Celestial Pole” (PSc), and the Equator becomes the “Celestial Equator”. The circles parallel to the Equator, on Earth called Parallels, in the Celestial Sphere are called “Parallels of Declination”, the circles parallel to the observer’s horizon are called “Almicantarat”.
Exactly as on Earth we orient ourselves with the compass and the North Pole, with astronomical navigation we orient ourselves with the angle at the pole between the star and the reference pole, or with the Zenith which would be the axis that crosses the observer, Zenit at the top and Nadir at its opposite. Just as the Earth’s axis passes through the Earth, an axis passes through the observer using perspective as if he were “the pole”. Today’s astronomical navigation is done by making observations with the sextant, calculations with the formulas of Euler and Neper’s theorems and the data taken from the Nautical Almanac and Nautical Tables, and by tracing the graph of the height lines. In this way we can find our position even when sailing far from the coast in the open sea, and the route to follow. More or less it has always been done like this, considering that Euler lived in 1700 and Neper about a century before him between 1500 and 1600, in ancient times instruments were still used for the detection of the Stars and sufficient knowledge to be able to determine the position of the ship and the route to follow. After the technological boom of the last century, especially in the last twenty years between 1980 and 2000, ships were equipped with so many technological devices (Radar, GPS, AIS, LRT, etc.), that many colleges and nautical schools, even some naval academies have decided to eliminate courses and lessons in astronomical navigation, considering it obsolete and useless. In truth this is not the case, indeed, even today in international conventions all devices and technological equipments are defined as “navigation aids” and are not mandatory, while the compass and log remain mandatory. In short, if a ship in port does not have a GPS, in theory the ship cannot be stopped by the authorities, while if lacks a compass they stop the ship and the captain must take the compass on board to obtain clearance for departure. It must also be considered that geolocation satellites are private or national, they have no obligation to provide the service, and above all they can be deactivated or obscured at any time and for any reason, especially for security reasons. Just an example, if a nation goes to war, feels threatened or has imminent security threats is detected, they can disable or black out its satellites and stop providing service. Considering that today the devices on the bridge are also interfaced, and that therefore the malfunction or deactivation of an instrument also causes problems in the other devices, today astronomical navigation still remains a safety feature for the conduction of the ship. Astronomical navigation is “coming back into fashion”, even the nautical schools and naval academies that had removed it from courses now have readmitted it and are starting to give lessons again. After all, in addition to being beautiful, romantic, ancient in its maritime traditions, it is also a security for all masters who venture out to sea. Even today, two astronomical measurements are made a day on board Italian ships and on the bridge the officers write, often on the chart table, “The stars never lie”.
Perhaps you mean Napier, not Neper?