The Economist have just published a letter I wrote to them regarding a recent academic article on Viking sunstones.
In the following letter I put forward what I believe to be an original argument on this popular subject. I have no way of proving this theory, which puts me in good company with the scientists who like to come up with new theories on this topic on an almost annual basis. I do at least know what it feels like to hear salt and ice fall from my beard, which may mark it as a little different.
The Viking’s use of sunstones has captured the imagination of scientists more frequently than these stones may have been used practically at sea (“Crystal Gazing”, March 9th).
There are good reasons why sunstones are unlikely navigation aids, and equally good ones why they may still have been carried on ships.
Direct sunlight is not polarised; it is sunlight that has been reflected, refracted or scattered (hence polarised sunglasses are effective at screening out glare when sailing or skiing). In practice polarised light comes from a very different part of the sky to the sun itself, typically a wide band perpendicular to the sun.
I cannot envisage a situation where a sunstone would do a good job. However, sunstones may have been carried by Viking navigators for a different reason. Just as successful generals need their troops to believe they possess extraordinary skills, so navigators in the age before the compass needed sailors to believe they too had skills that went well beyond the normal.
My belief, formed in the North Atlantic and not the laboratory, is that the Vikings relied on the many clues in nature, including the sun and birds, to navigate effectively (see my recent paper, “Nature’s Radar“, for the Royal Institute of Navigation). They may have relied on the sunstone and other legendary routines and rituals to get people to follow them confidently in difficult conditions.
It is possible that you may be mistaken in your comment on how impractical a sunstone may be to a navigator; especially in foggy overcast conditions. In the book “Secrets of the Viking Navigators” by Leif K. Karlsen, goes into much detail and has at least one practical test to show that a sunstone can accurately (to one degree) determine the direction of an unseen sun (below horizon/foggy conditions).
Perhaps you might like to investigate this further.
(a natural navigator from down-under)
Thanks for your email. I’m familiar with Leif Karlsen’s work and cite it in my book, The Natural Navigator.
However, my main argument would not be that it is impossible to use a sunstone to help find the direction of the sun, it is really that the number of times when this would have formed an expedient practical solution may be very seriously limited.
One of the main problems is that it could really only earn its keep in times of very dense fog, sufficiently dense that I would be surprised if a sunstone could work effectively. I have navigated using the reflection of the sun off the water in fairly dense fog a number of times in British coastal waters, it is surprisingly straightforward (see the line of the sun in the image below, which I took off the south coast of England a few years ago).
The other major problems concern type of fog and time. There are two common types of sea fog which will give a nautical navigator problems and they pose totally different challenges. A fog will usually only plague a navigator for long periods during becalmed times (we were becalmed in fog for 24 hours off Iceland last summer). So it can be seen that Vikings would have no use at all for a sunstone in such conditions, except perhaps a bit of fun.
A stronger wind and associated advection fog, formed when moist air is blown into an area with wind is potentially a problem. But since the navigator already has a wind and waves/swell to work with in these conditions we have to ask what use the sunstone might be. Also, since such a fog comes in with a wind, it tends not to stick around for long periods but often blows itself away in hours.
Another real problem is time. A navigator in advection fog could hold a dependable course relative to the wind and waves without serious concern for several hours. The only problem is likely to come if the fog lasts for a much longer time. However, a fog lasting a couple of days poses an entirely different problem to someone in these northern latitudes in summer.
Working out the direction of the sun is of no use to a navigator at all if he could not be confident of the time. Or is the argument being made that the Vikings took altitude and azimuth bearings using the sunstone to establish both bearing and time, referring to tables of some kind?
At these latitudes the gently fluctuating light levels of the sun in fog during the midsummer days would offer only the vaguest of clues. Near Iceland the difference between midnight and midday in June is fairly obvious, by temperature and light, but much more refined estimates in fog I think would be impossible. It may conceivably be possible to work out the sun direction using a sunstone and then estimate the time of day to within 3 hours, at which point you have a bearing of the sun accurate to within approximately 45 degrees in either direction. Why not use the wind and water which will nearly always give you a better estimate of direction than that?
Unless your real aim is to keep a crew happy, amused and confident, whilst you get on with the serious business of finding a way through the fog by more practical means?
That said, every other sailing culture in the world that I have encountered or researched has a better tactic for dealing with bad visibility and navigation concerns in open water and that is to heave-to or drop sails and sit it out. The Vikings weren’t racing, so why wouldn’t they do the same?
It is a very modern preoccupation that journeys must go on. From the Pacific to the Mediterranean, sailors have long had a history of taking their time if things are not going well navigationally.