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Sunstone (medieval)

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95 pointsbenbreen7 comments

It's interesting to consider how such a navigational instrument could have been more reliable than a compass in the far north where magnetic deviation becomes a serious concern, but where incredibly long summer days provide an opportunity for a trained sunstone navigator to shine (pun intended).

That’s possible. I’m not an expert on navigation, but given that people didn’t have accurate maps, magnetic deviation might not have been as much of a problem. When leaving a port you only need to know what compass heading to follow to reach your destination, which you can learn by trial and error, and regardless of moderate magnetic deviations there will always be one such. It might not take you on an optimal route, but that’s less important than that it gets you there reliably.

Magnetic deviation might not have been an problem in a single year, but magnetic drift can be quite impactful even over a decade. It can be quite severe the further North you get which can really throw compass directions off. The airport in Fairbanks, Alaska changed its runway numbers in 2009 and will change then again in 2033[1]. This can represent anywhere between a 15-30 degree drift over the course of 20 years.

For anything more than a short jaunt (which you probably don’t need a compass for anyway), you would need to understand updated magnetic deviation regularly to navigate with confidence.

[1] https://www.ncei.noaa.gov/news/airport-runway-names-shift-ma...

I had no idea runway numbers worked like that. Thanks!

I don't think so when the magnetic deviation can vary considerably over the course of a single leg, as it does near the geomagnetic poles.

You can buy a birefringent (https://en.m.wikipedia.org/wiki/Birefringence) calcite crystal that are often sold at rock shops and give it a try.

Great use case example in the series Vikings.

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