On the Topic

Why do we still need astronavigation in the face of three independent satellite navigation systems? Can having a sextant on board increase safety and is the oft-repeated phrase from „good seamanship“ still an argument in favour of an astronavigation backup?

Most skippers today are travelling without an astronavigation backup and blindly trust the technology of their satellite navigation. Astronavigation – as it is officially and currently, in the age of artificial intelligence, still supposed to be used in an emergency – is a real imposition that nobody wants to have. However, if you want to get your licence to sail on the ocean, there is no way around studying the traditional method of astronavigation. Those who are not comfortable with self-study may have to pay for an expensive training course. Apart from expanding your general knowledge, which is always a benefit, the purpose of the course is primarily to pass the upcoming exam. A few weeks later, everything is forgotten anyway and all the benefits that were perhaps hoped for are lost.

Why is the principle of good seamanship, which states that there must ALWAYS be a backup system on board for every system, widely regarded as dispensable in the case of navigation? As honourable as the high helmsmanship of the last generation of seafarers before the satellite age was, continuing to use it unchanged as an emergency backup in our time was and is not a good idea. These graphical navigation methods were developed in the 19th century and were standard in global shipping for more than 150 years. Of course, precise analytical methods for determining location at sea were already known at that time, but they had to be discarded because there were no computers. However, that has changed. We are used to working with computers. Nobody wants to have to struggle with the tools and means of past generations today or in the future.

Satellite navigation failure is not impossible. Satellite signals can be disrupted or on-board systems can fail. Both have already happened and the unavailability of satellite navigation would immediately send a boat at sea back to the 19th century. The sea is not a safe place. What is needed is an astronavigation system that can be used ad hoc by anyone, without any knowledge of maths or astronomy and without having to carry a mountain of astronomical information. Its use must be self-explanatory, so to speak.

Exact navigation methods have been known since the 18th century and can be traced back to the work of famous mathematicians such as Leonhard Euler and Carl Friedrich Gauss. They are known as analytical methods. They make it possible to determine a location at sea from just two measured star altitudes, and exclusively by calculation. These methods are the only ones suitable for the automated determination of a global position, as is common in satellite navigation. The only difference in the application is that the image point distance of a navigation star must be measured manually from the earth using a sextant. In contrast to satellites, natural celestial bodies cannot transmit their distance using radio signals.

Many books have been written and articles published in specialist journals about astronavigation, and there are also numerous articles on the Internet. In addition, many computer programmes and apps are known to make navigating with celestial bodies easier. However, everything that can be found here always revolves around the Saint Hilaire altitude method. Those who book a course – which of course still exist – are offered nothing other than Hilaire in its various variants. However, this graphical approximation method no longer fits in with our times, where digitalisation and AI are prevalent. Should astronavigation therefore disappear completely? That would be going too far, because it is and remains a last and only rescue anchor. It is therefore much more important to make astronavigation suitable for our modern age. Ironically, however, this is only possible with the very old methods that were developed long before Saint Hilaire and have since been forgotten. It is therefore necessary to present them on a website like this and in a book. Because the graphical astronavigation of Thomas Sumner and Saint Hilaire has also become known as modern astronavigation, this web page has been given the title Postmodern Astronavigation.