When I set sail from Halifax, Nova Scotia, in late July 1973, to cross the Atlantic, there was only one reliable way to navigate a small boat across an ocean.

You had to use a sextant to measure the heights of the sun and stars above the horizon. You also needed a chronometer to determine the exact time of each sextant sight.  With these two bits of information, a Nautical Almanac and some sight reduction tables, you could plot your position on a chart. If you were skilful and the conditions were favourable, the fix might be accurate to within a few miles.  

Celestial navigation had changed little since the days of the great voyages of scientific discovery in the second half of the 18th century.

By coincidence it was also in 1973 that the US military began developing the satellite navigation system we now know as GPS.  It wasn’t the first such system but it represented a major step forward in terms of accuracy and sophistication.  And it was a really amazing technical achievement.  

At its heart is a network of satellites in precisely determined orbits each carrying their own atomic clocks.  GPS receivers pick up the faint signals from these satellites and use them to fix their positions in three dimensions.

Of course I knew nothing of these developments.  I suppose I may have been dimly aware that the US military were already using some kind of satellite navigation – as indeed they were – but the Cold War was still very much in progress and such technology was highly sensitive.  That was to change when the Iron Curtain was lifted in 1989 and the Soviet Union fell apart.  

GPS was publicly available in the 1990s and in 2000 some controls were lifted so that the public had access to even better positional information.  Anyone who could buy a GPS receiver could now fix his or her position to within a few meters anyway on the surface of the earth. It was quite incredible at first but it soon became routine and familiar.

Since 2000, as the price (and size) of GPS receivers has dropped, this astonishing navigational technology has swept the board.  It’s everywhere: in our mobile phones, our cars, in planes and of course in boats.  We can even put GPS transponders in our valuables or on our children so that we can keep track of where they are!  

And now there are other satellite navigation systems besides GPS: notably the Russian GLONASS; China’s BEIDOU; and the European Union’s GALILEO. Collectively these are known as Global Navigation Satellite Systems or GNSS.

GNSS has made life much easier and, in many ways, much safer.  But it has its shortcomings.  First of all, it’s very vulnerable to interference and can easily be jammed.  Secondly, it’s quite easy to ‘spoof’ the GNSS signals and persuade a receiver that it’s somewhere where it’s not. For these reasons – and others – robust backup systems are badly needed.  One possibility is LORAN – an old radio-based navigation system developed in World War II.

Of course the most robust alternative to GNSS is the good old sextant.  It doesn’t even need electricity. But while many offshore sailors still study the principles of celestial navigation, very few make regular use of it. For most it is only a back-up system, to be called on in the supposedly unlikely event that GNSS fails.

The trouble is that celestial navigation is a skill, and like all skills it requires practice. I wonder how many offshore sailors could actually fix their position with a sextant if they had to do so in a hurry?

But leaving aside questions of safety, one of the sad consequences of the dominance of GNSS is that few people now learn how rewarding the practice of celestial navigation can be.

As I wrote in my book Sextant:

‘It is time to rediscover the joys of celestial navigation, not merely as a safety net, but because using a sextant to find our way puts us into the closest possible touch with the natural world at its most sublime.’

That’s still true, of course, but I don’t think many people are following my advice. Pushing buttons is just too easy.