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Rudi Kiefer: Why your compass may not really be pointing north
Rudi Kiefer

When there’s no GPS available, an old-fashioned magnetic compass is a great tool for orientation.  One problem is that the needle doesn’t exactly point north. The compass doesn’t know where the Earth’s North Pole is – that spot where all the meridians of longitude come together and mark geographic north. The needle is controlled by the Earth’s magnetic field. Imagine a giant bar magnet inside the planet, with a north and a south pole. Seen from Georgia, its north pole is roughly in the direction of the Arctic Ocean. The difference between “true north” and “magnetic north” is called needle declination, or compass error. Using a compass in California yields quite a different direction than it does over here. In North Georgia, declination is negative. That means the needle points to the left of true north, requiring an adjustment of about 5 degrees of angle. In San Francisco, the compass shows positive error, pointing 13 degrees to the right of true north. That’s a more serious difference, and compass users need to keep it in mind.

Another problem is that the Earth’s magnetic pole doesn’t sit still. Most of the planet consists of hot liquid magma, and there are currents deep inside that move it around. Until a few years ago, the magnetic pole was at the northern fringe of Canada. Currently, it’s crossing the Arctic Ocean and wandering towards Siberia. Its movement has been accelerating rapidly. Until the 1990’s, it was 9 miles per year.  Now, the pole is racing across the Arctic at 34 miles annually. That’s 4 inches per minute – a blazing fast speed for earth processes.  The rapid change forced the National Oceanic and Atmospheric Administration to rework its global magnetic model a year earlier than scheduled.

The reasons for the erratic behavior of the magnetic field, and the capricious movement of its poles, are unknown.  Some students might be quick to blame climate change, but that has nothing to do with movements deep inside the Earth’s core.

If you feel you don’t trust the compass at all, here’s an old outdoors method for telling direction if you have a wristwatch with hands. Point the small hand in the direction of the sun. At noon, that’s pretty close to south. At other times, south is halfway between the current hour and the 12 o’clock mark on the dial.

 

Rudi Kiefer, Ph.D., is a professor at Brenau University, teaching physical and health sciences on Brenau’s Georgia campuses and in China. His column appears Sundays and at gainesvilletimes.com.

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