Thursday, 14 March 2013

The legendary Sunstone- found at last?

Researchers say this crystal proves fabled Viking sunstones really did exist. (© Alderney Museum)

One report says it is something out of an Indiana Jones movie. The discovery that the crystal- first found aboard a British shipwreck off the Channel Islands thirty years ago- may be the fabled Icelandic ‘sunstone’  which helped Vikings navigate even in overcast skies far away from land. Researchers say that the discovery may be proof that the Viking sunstones really existed. Others have long suggested that the reason no sunstones have been found in Viking burial sites was because they cremated their people, thus destroying the crystal.

It is believed that the sunstone, because of its polarising and refracting qualities, helped the Vikings to follow the azimuth of the sun with remarkable accuracy. The crystal has been mentioned in the inventories of monasteries and churches, and in Viking folklore.  

Because of the rhombohedral shape of calcite crystals, "they refract or polarise light in such a way to create a double image," explains Mike Harrison of the Alderney Maritime Trust. This means that if you were to look at someone's face through a clear chunk of Icelandic spar, you would see two faces. But if the crystal is held in just the right position, the double image becomes a single image and you know the crystal is pointing east-west, Harrison said.

The sunstone found now (see pic above) was from the Alderney, a British warship that sank in 1592; scientists say that the substance is made of clacite. Physicist Guy Ropars says in ‘The Independent” that the crystal “could really have been used as an accurate optical sun compass as an aid to ancient navigation. It permits the observer to follow the azimuth of the sun, far below the horizon with an accuracy as great as plus or minus one degree.” 

Researchers have long believed that the magnetic compass was not fully understood by European seafarers until the end of the 16th century, even though it was introduced in the 13th; the sunstone may have been a good addition to the navigational armoury, and may have been in use even well after the magnetic compass was invented. The fact that the sunstone was found near navigational dividers suggests that it was still in use.

"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,"  researchers said in a publication. 


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