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    Sun Compass-Interesting Use
    From: Bruce J. Pennino
    Date: 2019 Apr 11, 20:14 -0700

    Hello All:

    I just finished re-reading Simon Winchester's  book "Krakatoa-The Day the World Exploded August 27 1883". It is really a book for those interested in geology,earth science, and continental drift. In the early 1960s, enough evidence from various branches of science had many believing continental drift was real. But there was limited definitive data. Winchester discussed in his book how he was a geology student and a  member of a Greenland sled team taking rock borings in basalt layers.There were many teams all over the world doing this. The six man sled teams had portable drills, camping equipment and took rock samples at many locations over the summer. They were on skis on the Iceland sheet.. Their goal was to obtain rock cores to evaluate Paleomagnetism in the volcanic rock layers (lava flows from millions of years earlier). It is well known that the north magnetic pole has moved around, and the details of movement have been determined. But it was also known that iron particles in molten lava align with the existing magnetic  North Pole. When the lava hardens there is a permanent record of the Pole's location at the time of the eruption.  With all the borings from all of the teams the magnetic alignments (compases) could be compared.  If the particles in the borings showed the borings had moved (relative to the location of the pole) over 30,000,000 years, the plate had moved and continental drift was proven. I herewith apologize for long and probably somewhat oversimplified and not toally accuarate introduction. They were at a latitude of about 70 N where it was well known that ordinary compasses were ineffective.

    As Simon wrote......." The compases are thus powerful forensic tools:They tell us where the poles are in relation to the rocks, or the rocks in relation to the poles,....." The team measured their "alignment"....."...... (we used) a very accurate sun compass to make sure we always knew where each sample lay to the present day poles". So I'm thinking they used dead reckoning, probably knew their latitude more or less (from land marks or maps, and used the sun compass to set their course and estimate longitude???? I've looked  online and a solar compass is accurate at best  to about one degree. What type of "very accurate " suncompass could they have used? I think he has tried to simplify the technical detail here because he uses the sun compass for the geographical pole.....then jumps to the ancient magnetic poles and present magnetic poles.

    Anyway, they can't be going very far each day on skiis. They are dragging tents , food , equipment etc. At 70N one degree of longitude is about 20.6 NM. If the sun compass measures to one degree, in their planning was  there some wishful thinking about their  true ground location? I would think they would want to determine their location more accurately: 0.25 degree or at least +/- 0.5 degree? Just wondering.

    When all the geologic data were evaluated, the sun compass accuracy did not matter too much( I think). It was determined that the Greenland Plate had moved about 15 degrees westward over 30,000,000 yearsor about 3/4 inch per year. 

    All thoughts please!

    Regards,

    Bruce

       
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