December 11, 2003
A: FROM MENTOR MOLLY WILLIAMS IN MI
Yes, a compass is just a magnetic needle mounted so that it can rotate easily. We know that opposite magnetic poles attract each other, so the magnetic compass needle and the earth, which is a giant magnet, attract each other. That means that the north pole of the compass magnet (defined as the end that points north) must be pointing toward a south magnetic pole that's located near the earth's geographic north pole. Actually, that magnetic pole is not exactly on the earth's geographic north pole, so people who use a magnetic compass to determine directions on the earth need to use correction tables to tell them how many degrees difference there is between magnetic north (the direction the compass points). In the middle of the US the error is only a few degrees, but as you get further north, the error is much bigger. Another interesting fact is that geologists have determined that the earth's magnetic field has changed directions many times. They know this because layers of volcanic rock became magnetized when they solidified, and they preserved the direction of earth's field at the time the rock layers were formed. And one more thing * the auroras (northern lights) that have been visible recently result from streams of charged particles ejected by the sun. The particles are directed to the magnetic poles of the earth where they ionize the atmosphere, causing the light show. That's why the auroras are usually seen only at latitudes near the north or south poles.