Mac Oglesby wrote
>There also was an article in Sky & Telescope magazine a while back which
>showed a sundial using polarized light from the sky. I can't lay my hands
>on the issue, but I believe it was about 18 months ago.
By a minor miracle I still have that article- thanks for the reminder about it.
It's called "Vikings and Polarization Sundials" in the May 97 issue pp91-94.
In addition to describing how to build a polarisation sundial, it suggests
that the Viking "sunstone" could have been a natural
birefringent crystal that enabled the suns position and hence
direction to be found from the polarisation of the sky. The article
quotes the Hrafns Saga (c1230) "the weather was thick and stormy...
The king looked about and saw no blue sky...then the king took
the sunstone and held it up, and he saw where [the sun] beamed
from the stone"
Les Cowley
Halos on the web
http://dspace.dial.pipex.com/lc/halo/halosim.htm
