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Q & A: Compass needle drift

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Most recent answer: 10/22/2007
Q:
does the exact position of a compass point change from day to day?
- daniel (age 12)
u.k.
A:
Hi Daniel,

Sure, but the changes due to the Earth's magnetic field changing are very slow. The molten core of the Earth, which makes the magnetic field, is flowing and changing constantly, but slowly. These changes are observable as motion in the magnetic poles of the Earth, and changes in the strength of the Earth's magnetic field.

Here's a about recent wanderings of the North magnetic pole. The pole may move by 10 to 40 kilometers in a year.

If you live very close to the pole, your compass needle might change a lot over a short amount of time. For example, if you lived 10 km from the pole and the pole moved from one side of your house to the other, your compass needle could swing all the way around and point the other way. Of course if you live that close to the Earth's magnetic pole, then the compass needle won't point north -- it'll point at the magnetic pole instead. It's a good approximation to call the compass needle's direction north for those of us who live far away from either the geographic pole or the magnetic north pole, but if you live close to either one, then you have to be careful with using your compass.

What might be more important, however, is the presence of anything magnetic nearby your compass. It may depend on whether a car's parked in your garage or not, or how many refrigerator magnets are close by.

Tom

(published on 10/22/2007)

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