Russell Kaye / Sandra-Lee Phipps / Getty Images Replica of a Viking ship by Greenland.

The legendary Viking sunstone that could accurately navigate the seven seas in bad weather may actually be based on a real artifact, claim scientists.

After spending three years examining a cloudy crystal discovered in an Elizabethan wreck, researchers believe it could have been used to locate the sun in cloudy weather. The Alderney sank off the British Channel Islands in 1592.

(PHOTOS: The Vikings Are Coming)

“In particular, at twilight when the sun is no longer observable being below the horizon, and the stars still not observable, this optical device could provide the mariners with an absolute reference in such situation,” wrote researchers in the Proceedings of the Royal Society A, a scientific journal.

A chemical analysis confirmed that the stone was calcite crystal, otherwise known as Icelandic Spar — believed to be the mineral of choice for Viking sunstones, reports Fox News.

Owing to the crystal’s unusual property of creating a double refraction of sunlight, the sun’s position can be pinpointed with remarkable accuracy simply by rotating it against the human eye until the darkness of the two shadows become equal. Researchers say the principle holds true even when obscured by thick cloud or fog.

It may not live up to its reputation as a magical gem that bestows the ability to plot the sun’s course even at night — as described in Icelandic fables — but the antique navigational aid could be behind the Vikings’ reputation as peerless explorers. Experts believe that Nordic adventurers may have beaten Columbus to the Americas by several centuries, according to the Independent.

The rectangular crystal has been studied by scientists at the University of Rennes, in Brittany, France, who suggests that Tudor sailors may also have used the stone hundreds of years after the end of the Viking Age.

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