How do Vikings use sunstones for navigation in cloudy or foggy conditions?

[M.KALEM]

I am studying about vikings navigation . Vikings use sunstones (e.g. tourmaline) for navigation in cloudy or foggy days. How can they do that? May be they can describe sun position with polarizer cyristal. If it is like that, What is the relationship between navigation and sun position?

 

[ideasrule]

See this: http://www.polarization.com/viking/viking.html

Essentially, the sky is polarized at 90 degrees to the Sun. If you get a polarizer, aim it at a certain piece of sky, and use it to find the polarization direction, the Sun will be in one of the perpendicular directions.

 

[M.KALEM]

why 90 degree? Which polarizer should I use? If I use tourmaline Will experiment be successful?