Navigation: Magical Stones of the Sun

Without benefit of compass, Viking sailors of the 9th century managed to ply their watery routes of conquest and commerce, navigating by stars at night and by sun during the day. No matter what the weather, according to ancient Scandinavian sagas, the sun could al ways be located with the aid of magical "sun stones." Summarizing sunstone lore in a recent article in the archaeology magazine Skalk, Danish Archaeologist Thorkild Ramskou lamented that none of the sagas clearly describe the sun stone. "But there seems to be a possibility," he wrote, "that it was an instrument which in clouded weather could show where the sun was."

Now, with a clue supplied by a young archaeology enthusiast, Ramskou has discovered the secret of the sun-seeking stones of the ancients. To the ten-year-old son of Jorgen Jensen, chief navigator of the Scandinavian Airlines System, the instrument described in Skalk sounded much like the twilight compass used by his father on flights at high latitudes, where the magnetic compass is unreliable. The twilight compass is equipped with a Polaroid filter that enables a navigator to locate the position of the sun—even when it is behind clouds or below the horizon—by the sunlight polarized by the atmosphere.

Flight test. Intrigued by his son's observation, Jensen passed it on to Ramskou, who immediately recognized its scientific implication. Enlisting the aid of Denmark's royal-court jeweler, the archaeologist collected minerals found in Scandinavia whose molecules are all aligned parallel to each other, just as the crystals are in a Polaroid filter. Ramskou found that one of these minerals, a transparent crystal called cordierite, turned from yellow to dark blue whenever its natural molecular alignment was held at right angles to the plane of polarized light from the sun. Thus, he reasoned, a Viking could have located the sun by rotating a chunk of cordierite until it turned dark blue.

Putting cordierite to the test, Ramskou accompanied Navigator Jensen on an SAS flight to Greenland, keeping track of the sun with his stone while Jensen used the twilight compass. His observations were accurate to within 21° of the sun's true position, and he was able to track the sun until it had dipped 7° below the horizon. "I now feel convinced," Ramskou concludes, "that the old Viking sailors with the aid of their sun stones could navigate with enormous accuracy."