No GPS? Who’s the guide ?

Did you know that the Ocean Globe Race in which we are going to compete doesn’t allow all types of geolocation system?

Indeed, we are not allowed to take a GPS with us to help us navigate. So, how are we going to find the way?


To answer that question, a lot of people would most likely say that a quick look at the sun or at the stars would help us navigate more or less. When you know where the sun rises, where it sets, and what way it takes in between, you’d have an idea of the direction you need to take. Nevertheless, it is quite obvious that this only approximation isn’t enough to manage sailing around the world! Indeed, to know where you need to go, you first have to make sure you know where you are!


Celestial navigation

It is obvious now that in order to prevent our captain to navigate straight until the North Pole, knowing our position in the first place is essential! Not allowed a GPS, we will rely on a much older-fashioned way to take us back where we started.


Watching the stars or the sun, is a much more accurate way to navigate than most people believe when you are prepared to it. Only, you have to watch closely. Moreover, it hasn’t been invented recently to respond to an emergency. It has indeed been used for a very long time in the sailing world before us.


As far as the history of humanity goes, it seems that we have always been keen on trying to answer the question of our origin, and by extension our location in the world.


Before humanity knew what a star was really made of, men already used them to find their way, know their position, deduce the time or even, calculate the earth’s circumference. And before going further in explaining the techniques that we are going to use to navigate, we thought that we ought to present you the astrolabe, an ingenious antique tool that takes a major place in the history of humanity’s geolocation.


The astrolabe, what is it ?

Figure 1 : Stéréographique Astrolabe . J.A. Linden, Heilbronn (Allemagne) © Royal Art and History Museum


An astrolabe is an elaborate inclinometer, and can be considered an analog calculator capable of working out several different kinds of problems in astronomy. The celestial archway is projected on the front side of the astrolabe in a similar way the globe is projected on a classic map. Sure the projection isn’t the result of the same calculations but still, the principle remains. It’s been invented by Hipparchus (greek astronomer c. 190 – c. 120 BC) and has been improved since according to its different purposes. The most common is the planispheric astrolabe.


Figure 2 :sides of an astrolabe


The one we are the most interested in among the different types of astrolabe is the nautical. It is a simpler version of the planispheric astrolabe and mainly allows the measurement of the celestial bodies. A simple calculation with a specific measure would give you instantly the latitude from which you made your observation. It has been developed by the Portuguese around the end of the fifteenth century.


Figure 3 : Nautical astrolabe. Considered to be one of the oldest known today. It has been made around the year 1500 and is made of very heavy bronze. Despite of the boat’s movement, its weight allowed it to keep steady even in rough seas when hanged as a plumb line. This astrolabe is currently kept in Gran Canaria within the collections of the « house-museum of Christopher Columbus ».










You might have guessed it now, the nautical astrolabe is actually the ancestor of the sextant. The sextant is indeed the tool that we will need out in the ocean to know our position!

Figure 4 : The sextant