The seafaring, farming, and military branches of ancient Norse society are the substance of enduring legends. The Vikings are known to have invaded, conquered, and settled much of the territory within the grasp of a significant societal component: seafaring. Their reach spanned much of northern and coastal Europe and radiated as far as North America, while talent in seafaring was also necessary for trade and harvesting foods. Talent in navigating fjords and oceans was essential to their cultural landscape and their societies’ ability to flourish between the 8th and 11th centuries.
The Vikings are stereotyped to have been primarily warlike, yet their intelligence and collected wisdoms had produced a singularly well-developed ability to navigate sea-faring vessels across vast distances. Navigation was arguably more important than the remarkable characteristics featured in an advanced and then-unmatched naval engineering ability. Many historical seafaring cultures used star charts, sundials, or bearing dials as navigational guides when the invention or presence of the magnetic compass was absent, yet Vikings may have had a unique edge: sun shadow boards paired with “sunstones.”
“Sunstones” appear in Norse histories and mythologies and were often assumed to be of the kind of fictitious allegory often found of legends. This is generally the fate of any subject involving a supernatural ability or trait being ascribed to an object – science designates a delineation between proven fact, correlative theory, and unsubstantiated idea. Sunstones are a rare case in which a ‘magical’ device most likely has a more-direct connection to reality than the allegories and metaphors found in fiction – or the historical forms of record keeping held within the storytelling of oral tradition. Unique among natural forms of nautical wayfinding of the historical era, sunstones functioned during daylight as their namesake suggests, producing a useful optical phenomenon when interacting with the light of the sun.
In ancient times, the navigators of ships could experience trouble whenever encountering cloudy days and nights. Lacking the accurate location of the sun, moon, or stars, and without failsafe devices like magnetic compasses, even the most experienced seafarers would have had to continuously guess their location and bearings over periods of darkness or extensive cloud cover. This scenario is where the sunstone is said to have ‘shined.’ Any individual sunstone (and it is expected by archeologists that there were indeed many of them) was likely a variety of the mineral calcite that modern geologists sometimes call ‘Iceland spar.’ Also called optical calcite, the mineral lends itself to navigation through its ability to depolarize sunlight. A good specimen would be covetted, the larger and most suitable sunstones being treasured and revered for their quality of the magic they were then thought to be imbued with and possess.
Some misinformation existed among historians and geologists had seemed to exist when defining sunstones – either as feldspar or as calcite. The kind of Iceland spar found in Viking shipwrecks (which characteristically produces the optical phenomenon linked to the legend), quickly settles this confusion. The two minerals share some properties, yet depolarization of light is a conclusive feature of optical calcite – a sunstone. Sunstones require some sunlight to function, so for the navigational purposes of Vikings, their magic could not be summoned during a storm. A small patch of blue sky, however, would suffice. Laurent Banguet describes the optical phenomenon and use of sunstones in an article published on Phys.org:
“…If you put a dot on top of the [calcite] crystal and look through it from below, two dots will appear. Then you rotate the crystal until the two points have exactly the same intensity or darkness. At that angle, the upward-facing surface indicates the direction of the Sun…”
“…A precision of a few degrees can be reached even under dark twilight conditions…. Vikings would have been able to determine with precision the direction of the hidden Sun…”
The ability for a navigator to gain bearings at sea with just a sliver of sunshine provided a competitive edge for Vikings by all measures, allowing them to outmaneuver the competition or simply navigate more directly, saving precious time and rations. Sunstones are thought to be merely one of many additional seafaring technologies used Vikings – along mainstays like cartography, naval instruments, mathematics, and the collected seafaring knowledge which informed their advanced shipbuilding toward the efficiency of their fleets.
There are disputes as to the exact implementation of Sunstone calcite crystals, as no direct or conclusive proof exists aside from modern conjectures tied to ancient written records. Some direct sunlight must be present for the sunstone to depolarize the light sufficiently, yet whenever a then-seafaring-grade sunstone was provided sufficient solar illumination so as to create the “two dots” phenomenon of depolarized sunlight, Viking sailors were essentially activating an optical compass. No other culture is known to have discovered and relied upon a compass of this kind. Knowing the sun’s location in the celestial sphere though the optical properties of a stone was a gift from the Old Gods – and still appears to the uninitiated as if a magic.
Neogeneses 