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    Re: Historical Magnetic Variation/Declination
    From: Bill B
    Date: 2004 Jun 14, 13:46 -0500

    > I had some time today to put together a few different ways of viewing the
    > historical magnetic declination/variation maps from the USGS....
    Very informative.  If I understand it correctly the earth reverses magnetic
    poles (approx. 100,000 year cycle?) and we are *way* overdue, with signs
    that this is starting to happen.  How quickly it happens is open to
    speculation, with an inconclusive study of volcanic lava flow indicating it
    has historically flipped in a matter of months in one case.
    Supposedly, while this reversal is happening, there are large areas of
    magnetic anomalies, with four, six, eight of more poles occurring worldwide.
    That could pretty well make a compass useless on an extended blue-water
    voyage.  But what about GPS or other satellite radio-based aids to
    I have totally lost signal for fifteen or more minutes at a stretch over the
    past year because of solar flares/magnetic storms that interfered with the
    radio transmissions from the satellites.
    Our current pole situation forms a shield from radiation which is weakest at
    the north and south poles.  If we have large areas of anomalies all over the
    planet, we also lose shielding in those areas.  How will this affect GPS
    I can't say I'm going to invest heavily in sextant manufactures' stock based
    on the above, but it does make a reasonable case for including celestial
    navigation in a mariner's study plan.
    Bill B.

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