You might think seafaring Vikings–who traveled hundreds of miles on rough seas between 750 and 1050 AD–would be adrift on cloudy days: not only did they lack compasses, but they were often traveling so far north that the sun never set, and thus couldn’t use stars to navigate. But scientists are finding new evidence to support the existence of what was once considered a mythical navigational tool: the sólarsteinn, or sunstone.
It all starts with an Icelandic legend about a man named Sigurd. As Nature News reports:
The saga describes how, during cloudy, snowy weather, King Olaf consulted Sigurd on the location of the Sun. To check Sigurd’s answer, Olaf “grabbed a sunstone, looked at the sky and saw from where the light came, from which he guessed the position of the invisible Sun.” In 1967, Thorkild Ramskou, a Danish archaeologist, suggested that this stone could have been a polarizing crystal such as Icelandic spar, a transparent form of calcite, which is common in Scandinavia.