Understanding
Magnetic Declination
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“Declination:
A Noun. The horizontal angle between the true geographic North Pole and the
magnetic North Pole, as figured from a specific point on the Earth.”
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Declination
is a term that causes “brain cramps” for many of my students in my map and
compass classes. When I mention Magnetic Declination eyes roll.
The
web site www.magnetic-declination.com has
an excellent discussion of what declination is and what causes it:
“Magnetic
declination varies both from place to place, and with the passage of time. As a
traveler cruises the east coast of the United States, for example, the
declination varies from 20 degrees west (in Maine) to zero (in Florida), to 10
degrees east (in Texas), meaning a compass adjusted at the beginning of the
journey would have a true north error of over 30 degrees if not adjusted for the
changing declination. The magnetic declination in a given area will change
slowly over time, possibly as much as 2-25 degrees every hundred years or so,
depending upon how far from the magnetic poles it is. Complex fluid motion in
the outer core of the Earth (the molten metallic region that lies from 2800 to
5000 km below the Earth's surface) causes the magnetic field to change slowly
with time.
To read the rest of the post go here.
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