LEGEND
In the Sigurd Legend Holy Olaf, the king sent out somebody to find the sun in the sky but they couldn't locate it.
The saga releates: 'Sigurd grabbed a sunstone, looked at the sky and saw from where the light came, from which he guessed the position of the invisible Sun. It turned out that Sigurd was right.
SCIENCE
It was thought that the expert Vikings navigators like the ancient Mediterranean seafarers used sundials or simply hugged the coastline on long journeys, however new research indicates otherwise:
The researchers say: 'Some types of crystal create birefringence - a double refraction of light.
By splitting light into ordinary and extraordinary rays we were able to work out where the Sun was and navigate through sunlit fog.
Experiments and tests were run with 'sunstones' in the Arctic, Finland, Hungary and Tunisia.
Vikings undoubtedly often had to sail under totally overcast conditions, perhaps for days on end in the open water far away from land,' said Dr Gabor Horvath.
'Using the crystal,' he reported that, 'to our great surprise, the patterns of the direction of polarisation under totally overcast skies were very similar to those under clear skies.
SOURCES
http://news.bbc.co.uk/1/hi/world/europe/6338535.stm
Metro newspaper, London England