Science Nerd
Finally, the page of
how it works. I will do my best to explain how
this second method of finding the sun was
performed and, more importantly, why it works.
The method itself is quite
simple and can be (sort of) clearly seen in this
video- http://www.youtube.com/watch?v=Rm3260yUJGw.
In the video, you can see the sun through the
crystal and probably realize that it is not very
difficult to locate. This is simply a
demonstration to show what to look for when
locating the sun. The same method works on
overcast days or during the last minutes of
twilight. To locate the sun, the viewer simply
places one dot on the face of a rhombohedral cut
piece of Iceland Spar. Then, on the opposite
face, the viewer will see two dots that change
in color and intensity as they spin in a circle.
If the general direction of the sun is found
with the Biological phenomenon or can be found
by general observation, to within 90 degrees,
then this method can pinpoint the sun's
location. In Figure 1b, the black dot between A
and B is our drawn dot. This shows what happens
to the ordinary and extraordinary rays at the
point of isotropy, K. When light hits calcite,
the light rays are depolarized, or separated
into different rays. The ordinary ray refracts
at the normal angle of refraction. The
extraordinary ray refracts at an angle relative
to the viewer. The point of isotropy, K, is the
point at which the light passing through the
crystal and into the viewers eye is completely
depolarized. Many strange things happen at this
point, including the best results for seeing the
yellow 'bow-tie' shape on the fovea that leads
to the sun, if a patch of blue sky is available.
Figure 2 shows that this point, K, is achieved
when the angle of the crystal is 45 degrees. As
seen in the video demonstration, the ordinary
ray becomes the darkest (has the highest
irradiance) as you move from the sun in one
direction and then the extraordinary rays
irradiance almost disappears. When moved in the
opposite direction, the irradiance values switch
between the two rays. From The Royal Societies
study, we have found that this angle is 45
degrees from the sun. This is why the range of
finding the sun is 90 degrees. When each of the
dots' images are identical in color and
intensity, the crystal is in the middle of this
range and the sun is, within 1 degree, in the
direction of the crystal's face.
Conclusion
There may not be a ton
of evidence that the Vikings used these
'sunstones' to navigate the open ocean. There
has not even been much experimentation or
uproar for this special crystal. But, after
recent discoveries in the past few years and
possibly more in the future, we could
eventually prove that the Vikings used some
form of calcite to navigate the open ocean.
One thing that is obvious to us now, however,
is that it is very possible and even plausible
that the most famous of ancient seafarers
could have discovered the near-magical
properties of this unique crystal.
