http://www.rmg.co.uk/explore/sea-and-ships/facts/ships-and-seafarers/the-vikingshttp://sciencenordic.com/how-vikings-navigated-world
http://cosmiclog.nbcnews.com/_news/2011/02/01/5968012-did-vikings-navigate-with-sunstone?lite
http://sciencenordic.com/how-vikings-navigated-world
http://cosmiclog.nbcnews.com/_news/2011/02/01/5968012-did-vikings-navigate-with-sunstone?lite
http://sciencenordic.com/how-vikings-navigated-world